diff --git a/ECS/Dispatcher/DispatcherOnChange.cs b/ECS/Dispatcher/DispatcherOnChange.cs
index 2a265d6..0601df8 100644
--- a/ECS/Dispatcher/DispatcherOnChange.cs
+++ b/ECS/Dispatcher/DispatcherOnChange.cs
@@ -2,9 +2,9 @@ using System.Collections.Generic;
 
 namespace Svelto.ECS
 {
-    public class DispatcherOnChange<T> : DispatcherOnSet<T>
+    public class DispatchOnChange<T> : DispatchOnSet<T>
     {
-        public DispatcherOnChange(int senderID) : base(senderID)
+        public DispatchOnChange(int senderID) : base(senderID)
         { }
 
         public new T value
diff --git a/ECS/Dispatcher/DispatcherOnSet.cs b/ECS/Dispatcher/DispatcherOnSet.cs
index 0514064..2c9f069 100644
--- a/ECS/Dispatcher/DispatcherOnSet.cs
+++ b/ECS/Dispatcher/DispatcherOnSet.cs
@@ -1,11 +1,13 @@
+using BetterWeakEvents;
+
 namespace Svelto.ECS
 {
-    public class DispatcherOnSet<T>
+    public class DispatchOnSet<T>
     {
-        public DispatcherOnSet(int senderID)
+        public DispatchOnSet(int senderID)
         {
             _senderID = senderID;
-            _subscribers = new System.Collections.Generic.HashSet<WeakAction<int, T>>();
+            _subscribers = new WeakEvent<int, T>();
         }
 
         public T value
@@ -14,14 +16,7 @@ namespace Svelto.ECS
             {
                 _value = value;
 
-                if (_subscribers != null)
-                {
-                    using (var enumerator = _subscribers.GetEnumerator())
-                    {
-                        while (enumerator.MoveNext() == true)
-                            enumerator.Current.Invoke(_senderID, _value);
-                    }
-                }
+                _subscribers.Invoke(_senderID, value);
             }
 
             get 
@@ -30,19 +25,19 @@ namespace Svelto.ECS
             }
         }
 
-        public void NotifyOnDataChange(System.Action<int, T> action)
+        public void NotifyOnValueSet(System.Action<int, T> action)
         {
-            _subscribers.Add(new WeakAction<int, T>(action));
+            _subscribers += action;
         }
 
-        public void StopNotifyOnDataChange(System.Action<int, T> action)
+        public void StopNotify(System.Action<int, T> action)
         {
-            _subscribers.Remove(new WeakAction<int, T>(action));
+            _subscribers -= action;
         }
 
         protected T      _value;
         protected int    _senderID;
 
-        protected System.Collections.Generic.HashSet<WeakAction<int, T>> _subscribers;
+        protected WeakEvent<int, T> _subscribers;
     }
 }
diff --git a/ECS/GenericEntityDescriptor.cs b/ECS/GenericEntityDescriptor.cs
new file mode 100644
index 0000000..16c2687
--- /dev/null
+++ b/ECS/GenericEntityDescriptor.cs
@@ -0,0 +1,127 @@
+namespace Svelto.ECS
+{
+    class GenericEntityDescriptor<T> : EntityDescriptor
+        where T : NodeWithID, new()
+    {
+        static GenericEntityDescriptor()
+        {
+            _nodesToBuild = new INodeBuilder[]
+            {
+                new NodeBuilder<T>()
+            };
+        }
+        public GenericEntityDescriptor(params object[] componentsImplementor) : base(_nodesToBuild, componentsImplementor)
+        {
+        }
+        static INodeBuilder[] _nodesToBuild;
+    }
+
+    class GenericEntityDescriptor<T, U> : EntityDescriptor
+        where T : NodeWithID, new()
+        where U : NodeWithID, new()
+    {
+        static GenericEntityDescriptor()
+        {
+            _nodesToBuild = new INodeBuilder[]
+            {
+                new NodeBuilder<T>(),
+                new NodeBuilder<U>()
+            };
+        }
+        public GenericEntityDescriptor(params object[] componentsImplementor) : base(_nodesToBuild, componentsImplementor)
+        {
+        }
+        static INodeBuilder[] _nodesToBuild;
+    }
+
+    class GenericEntityDescriptor<T, U, V> : EntityDescriptor
+        where T : NodeWithID, new()
+        where U : NodeWithID, new()
+        where V : NodeWithID, new()
+    {
+        static GenericEntityDescriptor()
+        {
+            _nodesToBuild = new INodeBuilder[]
+            {
+                new NodeBuilder<T>(),
+                new NodeBuilder<U>(),
+                new NodeBuilder<V>()
+            };
+        }
+        public GenericEntityDescriptor(params object[] componentsImplementor) : base(_nodesToBuild, componentsImplementor)
+        {
+        }
+        static INodeBuilder[] _nodesToBuild;
+    }
+
+    class GenericEntityDescriptor<T, U, V, W> : EntityDescriptor
+        where T : NodeWithID, new()
+        where U : NodeWithID, new()
+        where V : NodeWithID, new()
+        where W : NodeWithID, new()
+    {
+        static GenericEntityDescriptor()
+        {
+            _nodesToBuild = new INodeBuilder[]
+            {
+                new NodeBuilder<T>(),
+                new NodeBuilder<U>(),
+                new NodeBuilder<V>(),
+                new NodeBuilder<W>()
+            };
+        }
+        public GenericEntityDescriptor(params object[] componentsImplementor) : base(_nodesToBuild, componentsImplementor)
+        {
+        }
+        static INodeBuilder[] _nodesToBuild;
+    }
+
+    class GenericEntityDescriptor<T, U, V, W, X> : EntityDescriptor
+        where T : NodeWithID, new()
+        where U : NodeWithID, new()
+        where V : NodeWithID, new()
+        where W : NodeWithID, new()
+        where X : NodeWithID, new()
+    {
+        static GenericEntityDescriptor()
+        {
+            _nodesToBuild = new INodeBuilder[]
+            {
+                new NodeBuilder<T>(),
+                new NodeBuilder<U>(),
+                new NodeBuilder<V>(),
+                new NodeBuilder<W>(),
+                new NodeBuilder<X>()
+            };
+        }
+        public GenericEntityDescriptor(params object[] componentsImplementor) : base(_nodesToBuild, componentsImplementor)
+        {
+        }
+        static INodeBuilder[] _nodesToBuild;
+    }
+    class GenericEntityDescriptor<T, U, V, W, X, Y> : EntityDescriptor
+        where T : NodeWithID, new()
+        where U : NodeWithID, new()
+        where V : NodeWithID, new()
+        where W : NodeWithID, new()
+        where X : NodeWithID, new()
+        where Y : NodeWithID, new()
+    {
+        static GenericEntityDescriptor()
+        {
+            _nodesToBuild = new INodeBuilder[]
+            {
+                new NodeBuilder<T>(),
+                new NodeBuilder<U>(),
+                new NodeBuilder<V>(),
+                new NodeBuilder<W>(),
+                new NodeBuilder<X>(),
+                new NodeBuilder<Y>()
+            };
+        }
+        public GenericEntityDescriptor(params object[] componentsImplementor) : base(_nodesToBuild, componentsImplementor)
+        {
+        }
+        static INodeBuilder[] _nodesToBuild;
+    }
+}
diff --git a/Utilities/WeakAction.cs.meta b/ECS/GenericEntityDescriptor.cs.meta
similarity index 75%
rename from Utilities/WeakAction.cs.meta
rename to ECS/GenericEntityDescriptor.cs.meta
index eb12418..840728d 100644
--- a/Utilities/WeakAction.cs.meta
+++ b/ECS/GenericEntityDescriptor.cs.meta
@@ -1,6 +1,6 @@
 fileFormatVersion: 2
-guid: eaffccbdbcacfa449b997dc1f7181bb4
-timeCreated: 1461942385
+guid: fd70d1b3107162f4790b1b71a129818f
+timeCreated: 1484485852
 licenseType: Pro
 MonoImporter:
   serializedVersion: 2
diff --git a/ECS/Sequencer.cs b/ECS/Sequencer.cs
new file mode 100644
index 0000000..f9d0efd
--- /dev/null
+++ b/ECS/Sequencer.cs
@@ -0,0 +1,52 @@
+using System;
+using Steps = System.Collections.Generic.Dictionary<Svelto.ECS.IEngine, System.Collections.Generic.Dictionary<System.Enum, Svelto.ECS.IStep[]>>;
+
+namespace Svelto.ECS
+{
+    public interface IStep
+    { }
+
+    public interface IStep<T>:IStep
+    {
+        void Step(ref T token, Enum condition);
+    }
+
+    public class Sequencer
+    {
+        public Sequencer()
+        {}
+
+        public void SetSequence(Steps steps)       
+        {
+            _steps = steps;
+        }
+
+        public void Next<T>(IEngine engine, ref T param)
+        {
+            Next(engine, ref param, Condition.always);
+        }
+
+        public void Next<T>(IEngine engine, ref T param, Enum condition)
+        {
+            var tos = _steps[engine];
+            var steps = tos[condition];
+
+            if (steps != null)
+                for (int i = 0; i < steps.Length; i++)
+                    ((IStep<T>)steps[i]).Step(ref param, condition);
+        }
+
+        Steps     _steps;
+    }
+
+    public enum Condition
+    {
+        always
+    }
+
+    public enum DamageCondition
+    {
+        damage,
+        dead
+    }
+}   
\ No newline at end of file
diff --git a/ECS/Sequencer.cs.meta b/ECS/Sequencer.cs.meta
new file mode 100644
index 0000000..87596cb
--- /dev/null
+++ b/ECS/Sequencer.cs.meta
@@ -0,0 +1,12 @@
+fileFormatVersion: 2
+guid: 4e1f40937ca5027428ed7193729be1a5
+timeCreated: 1484487023
+licenseType: Pro
+MonoImporter:
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/ECS/SingleNodeEngine.cs b/ECS/SingleNodeEngine.cs
index 6b43243..f888ee2 100644
--- a/ECS/SingleNodeEngine.cs
+++ b/ECS/SingleNodeEngine.cs
@@ -12,7 +12,9 @@
             Remove(obj as TNodeType);
         }
 
-        protected abstract void Add(TNodeType node);
-        protected abstract void Remove(TNodeType node);
+        protected virtual void Add(TNodeType node)
+        {}
+        protected virtual void Remove(TNodeType node)
+        {}
     }
 }
diff --git a/Utilities/WeakAction.cs b/Utilities/WeakAction.cs
deleted file mode 100644
index 0264419..0000000
--- a/Utilities/WeakAction.cs
+++ /dev/null
@@ -1,99 +0,0 @@
-using System;
-using System.Reflection;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-
-public struct WeakAction<T1, T2>:IEquatable<WeakAction<T1, T2>>
-{
-    public WeakAction(Action<T1, T2> listener)
-    {
-        ObjectRef = GCHandle.Alloc(listener.Target, GCHandleType.Weak);
-        Method = listener.Method;
-
-        if (Method.DeclaringType.GetCustomAttributes(typeof(CompilerGeneratedAttribute), false).Length != 0)
-            throw new ArgumentException("Cannot create weak event to anonymous method with closure.");
-    }
-
-    public bool Invoke(T1 data1, T2 data2)
-    {
-        if (ObjectRef.IsAllocated && ObjectRef.Target != null)
-        {
-            Method.Invoke(ObjectRef.Target, new object[] { data1, data2 });
-            return true;
-        }
-
-        return false;
-    }
-
-    public bool Equals(WeakAction<T1, T2> other)
-    {
-        return (Method.Equals(other.Method));
-    }
-
-    readonly GCHandle   ObjectRef;
-    readonly MethodInfo Method;
-}
-
-public struct WeakAction<T>:IEquatable<WeakAction<T>>
-{
-    public WeakAction(Action<T> listener) 
-    {
-        ObjectRef = GCHandle.Alloc(listener.Target, GCHandleType.Weak);
-        Method = listener.Method;
-
-        if (Method.DeclaringType.GetCustomAttributes(typeof(CompilerGeneratedAttribute), false).Length != 0)
-            throw new ArgumentException("Cannot create weak event to anonymous method with closure.");
-    }
-
-    public bool Invoke(T data)
-    {
-        if (ObjectRef.IsAllocated && ObjectRef.Target != null)
-        {
-            Method.Invoke(ObjectRef.Target, new object[] { data });
-            return true;
-        }
-
-        return false;
-    }
-
-    public bool Equals(WeakAction<T> other)
-    {
-        return (Method.Equals(other.Method));
-    }
-
-    readonly GCHandle   ObjectRef;
-    readonly MethodInfo Method;
-}
-
-public struct WeakAction:IEquatable<WeakAction>
-{
-    public WeakAction(Action listener) 
-    {
-        ObjectRef = GCHandle.Alloc(listener.Target, GCHandleType.Weak);
-        Method = listener.Method;
-
-        if (Method.DeclaringType.GetCustomAttributes(typeof(CompilerGeneratedAttribute), false).Length != 0)
-            throw new ArgumentException("Cannot create weak event to anonymous method with closure.");
-    }
-
-    public bool Invoke()
-    {
-        if (ObjectRef.IsAllocated && ObjectRef.Target != null)
-        {
-            Method.Invoke(ObjectRef.Target, null);
-            return true;
-        }
-
-        return false;
-    }
-
-    public bool Equals(WeakAction other)
-    {
-        return (Method.Equals(other.Method));
-    }
-
-    readonly GCHandle   ObjectRef;
-    readonly MethodInfo Method;
-}
-
-
diff --git a/Utilities/WeakActionStruct.cs b/Utilities/WeakActionStruct.cs
new file mode 100644
index 0000000..17158e1
--- /dev/null
+++ b/Utilities/WeakActionStruct.cs
@@ -0,0 +1,122 @@
+using System;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+//careful, you must handle the destruction of the GCHandles!
+
+namespace BetterWeakEvents
+{
+    public struct WeakAction<T1, T2> : IEquatable<WeakAction<T1, T2>>
+    {
+        public WeakAction(Action<T1, T2> listener)
+        {
+            ObjectRef = GCHandle.Alloc(listener.Target, GCHandleType.Weak);
+            Method = listener.Method;
+
+            if (Method.DeclaringType.GetCustomAttributes(typeof(CompilerGeneratedAttribute), false).Length != 0)
+                throw new ArgumentException("Cannot create weak event to anonymous method with closure.");
+        }
+
+        public bool Invoke(T1 data1, T2 data2)
+        {
+            if (ObjectRef.IsAllocated && ObjectRef.Target != null)
+            {
+                Method.Invoke(ObjectRef.Target, new object[] { data1, data2 });
+                return true;
+            }
+
+            Release();
+            return false;
+        }
+
+        public bool Equals(WeakAction<T1, T2> other)
+        {
+            return (Method.Equals(other.Method));
+        }
+
+        public void Release()
+        {
+            ObjectRef.Free();
+        }
+
+        readonly GCHandle ObjectRef;
+        readonly MethodInfo Method;
+    }
+
+    public struct WeakAction<T> : IEquatable<WeakAction<T>>
+    {
+        public WeakAction(Action<T> listener)
+        {
+            ObjectRef = GCHandle.Alloc(listener.Target, GCHandleType.Weak);
+            Method = listener.Method;
+
+            if (Method.DeclaringType.GetCustomAttributes(typeof(CompilerGeneratedAttribute), false).Length != 0)
+                throw new ArgumentException("Cannot create weak event to anonymous method with closure.");
+        }
+
+        public bool Invoke(T data)
+        {
+            if (ObjectRef.IsAllocated && ObjectRef.Target != null)
+            {
+                Method.Invoke(ObjectRef.Target, new object[] { data });
+                return true;
+            }
+
+            Release();
+            return false;
+        }
+
+        public bool Equals(WeakAction<T> other)
+        {
+            return (Method.Equals(other.Method));
+        }
+
+        public void Release()
+        {
+            ObjectRef.Free();
+        }
+
+        readonly GCHandle ObjectRef;
+        readonly MethodInfo Method;
+    }
+
+    public struct WeakAction : IEquatable<WeakAction>
+    {
+        public WeakAction(Action listener)
+        {
+            ObjectRef = GCHandle.Alloc(listener.Target, GCHandleType.Weak);
+            Method = listener.Method;
+
+            if (Method.DeclaringType.GetCustomAttributes(typeof(CompilerGeneratedAttribute), false).Length != 0)
+                throw new ArgumentException("Cannot create weak event to anonymous method with closure.");
+        }
+
+        public bool Invoke()
+        {
+            if (ObjectRef.IsAllocated && ObjectRef.Target != null)
+            {
+                Method.Invoke(ObjectRef.Target, null);
+                return true;
+            }
+
+            Release();
+            return false;
+        }
+
+        public bool Equals(WeakAction other)
+        {
+            return (Method.Equals(other.Method));
+        }
+
+        public void Release()
+        {
+            ObjectRef.Free();
+        }
+
+        readonly GCHandle ObjectRef;
+        readonly MethodInfo Method;
+    }
+
+
+}
\ No newline at end of file
diff --git a/Utilities/WeakActionStruct.cs.meta b/Utilities/WeakActionStruct.cs.meta
new file mode 100644
index 0000000..49656b3
--- /dev/null
+++ b/Utilities/WeakActionStruct.cs.meta
@@ -0,0 +1,12 @@
+fileFormatVersion: 2
+guid: 1662357721652524593d7b0f731aef45
+timeCreated: 1484483913
+licenseType: Pro
+MonoImporter:
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/Utilities/WeakEvent.cs b/Utilities/WeakEvent.cs
new file mode 100644
index 0000000..e912490
--- /dev/null
+++ b/Utilities/WeakEvent.cs
@@ -0,0 +1,35 @@
+using Svelto.DataStructures;
+using System;
+
+namespace BetterWeakEvents
+{
+    public class WeakEvent<T1, T2>
+    {
+        public static WeakEvent<T1, T2> operator+(WeakEvent<T1, T2> c1, Action<T1, T2> x)
+        {
+            c1._subscribers.Add(new WeakAction<T1, T2>(x));
+            return c1;
+        }
+
+        public static WeakEvent<T1, T2> operator-(WeakEvent<T1, T2> c1, Action<T1, T2> x)
+        {
+            c1._subscribers.UnorderredRemove(new WeakAction<T1, T2>(x));
+            return c1;
+        }
+
+        public void Invoke(T1 arg1, T2 arg2)
+        {
+            for (int i = 0; i < _subscribers.Count; i++)
+                if (_subscribers[i].Invoke(arg1, arg2) == false)
+                    _subscribers.UnorderredRemoveAt(i--);
+        }
+
+        ~WeakEvent()
+        {
+            for (int i = 0; i < _subscribers.Count; i++)
+                _subscribers[i].Release();
+        }
+
+        protected FasterList<WeakAction<T1, T2>> _subscribers = new FasterList<WeakAction<T1, T2>>();
+    }
+}
\ No newline at end of file
diff --git a/Utilities/WeakEvent.cs.meta b/Utilities/WeakEvent.cs.meta
new file mode 100644
index 0000000..884293e
--- /dev/null
+++ b/Utilities/WeakEvent.cs.meta
@@ -0,0 +1,12 @@
+fileFormatVersion: 2
+guid: e2ee3763e7dffd4459c588eda6867ddd
+timeCreated: 1484480295
+licenseType: Pro
+MonoImporter:
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: