diff --git a/src/ECS.Boost/Friflo.Engine.ECS.Boost.csproj b/src/ECS.Boost/Friflo.Engine.ECS.Boost.csproj
index 2ac010fa..2ab3c254 100644
--- a/src/ECS.Boost/Friflo.Engine.ECS.Boost.csproj
+++ b/src/ECS.Boost/Friflo.Engine.ECS.Boost.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>library</OutputType>
-    <TargetFrameworks>net8.0;net7.0;net6.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>net8.0;net7.0;net6.0;netstandard2.1;netstandard2.0</TargetFrameworks>
     <ImplicitUsings>disable</ImplicitUsings>
     <Nullable>disable</Nullable>
     <RootNamespace>Friflo.Engine.ECS</RootNamespace>
diff --git a/src/ECS/Archetype/EntityStore.Archetype.cs b/src/ECS/Archetype/EntityStore.Archetype.cs
index 59c150a1..273def6f 100644
--- a/src/ECS/Archetype/EntityStore.Archetype.cs
+++ b/src/ECS/Archetype/EntityStore.Archetype.cs
@@ -186,7 +186,11 @@ internal static void AddArchetype (EntityStoreBase store, Archetype archetype)
         }
         store.archs[store.archsCount] = archetype;
         store.archsCount++;
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+        store.archSet.Add(archetype.key, archetype.key);
+#else
         store.archSet.Add(archetype.key);
+#endif
     }
     #endregion
 }
diff --git a/src/ECS/Archetype/EntityStore.cs b/src/ECS/Archetype/EntityStore.cs
index 6c1a32fc..a6a5ba75 100644
--- a/src/ECS/Archetype/EntityStore.cs
+++ b/src/ECS/Archetype/EntityStore.cs
@@ -78,7 +78,11 @@ public abstract partial class EntityStoreBase
     // --- archetypes
     [Browse(Never)] internal            Archetype[]             archs;              //  8   - array of all archetypes. never null
     [Browse(Never)] private             int                     archsCount;         //  4   - number of archetypes
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+    [Browse(Never)] private  readonly   Dictionary<ArchetypeKey, ArchetypeKey> archSet; //  8   - Set<> to get archetypes by key
+#else
     [Browse(Never)] private  readonly   HashSet<ArchetypeKey>   archSet;            //  8   - Set<> to get archetypes by key
+#endif
     /// <summary>The default <see cref="Archetype"/> has no <see cref="Archetype.ComponentTypes"/> and <see cref="Archetype.Tags"/>.<br/>
     /// Its <see cref="Archetype"/>.<see cref="Archetype.archIndex"/> is always 0 (<see cref="Static.DefaultArchIndex"/>).</summary>
     [Browse(Never)] internal readonly   Archetype               defaultArchetype;   //  8   - default archetype. has no components & tags
@@ -142,7 +146,11 @@ internal static class Static
     protected EntityStoreBase()
     {
         archs               = new Archetype[2];
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+        archSet             = new Dictionary<ArchetypeKey, ArchetypeKey>(ArchetypeKeyEqualityComparer.Instance);
+#else
         archSet             = new HashSet<ArchetypeKey>(ArchetypeKeyEqualityComparer.Instance);
+#endif
         var config          = GetArchetypeConfig(this);
         defaultArchetype    = new Archetype(config);
         searchKey           = new ArchetypeKey();
diff --git a/src/ECS/Base/SchemaUtils.cs b/src/ECS/Base/SchemaUtils.cs
index e089fc71..99808b1b 100644
--- a/src/ECS/Base/SchemaUtils.cs
+++ b/src/ECS/Base/SchemaUtils.cs
@@ -18,7 +18,11 @@ private static bool RegisterComponentTypesByReflection() {
         if (Platform.IsUnityRuntime) {
             return true;
         }
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+        return true;
+#else
         return System.Runtime.CompilerServices.RuntimeFeature.IsDynamicCodeCompiled;
+#endif
     }
     
     [ExcludeFromCodeCoverage]
diff --git a/src/ECS/Entity/MemberPath.cs b/src/ECS/Entity/MemberPath.cs
index 555fa53b..2bfb58b2 100644
--- a/src/ECS/Entity/MemberPath.cs
+++ b/src/ECS/Entity/MemberPath.cs
@@ -104,6 +104,10 @@ private MemberPath(MemberPathKey key, ComponentType componentType, int structInd
     
     private const BindingFlags Flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.GetProperty;
     
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+    private static readonly char[] SplitDotArray = ['.'];
+#endif
+    
     /// <summary>
     /// Returns a <see cref="MemberPath"/> identifying a specific field / property by its <paramref name="path"/>
     /// within the passed <paramref name="type"/>.
@@ -122,7 +126,11 @@ public static MemberPath Get(Type type, string path)
         if (Map.TryGetValue(key, out var componentFieldInfo)) {
             return componentFieldInfo;
         }
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+        var pathItems   = path.Split(SplitDotArray, StringSplitOptions.RemoveEmptyEntries);
+#else
         var pathItems   = path.Split('.', StringSplitOptions.RemoveEmptyEntries);
+#endif
         var memberInfos = new MemberInfo[pathItems.Length];
         var memberType  = type;
         bool canWrite   = true;
@@ -188,10 +196,24 @@ public static MemberPath Get(Type type, string path)
     
     // See ThrowIfTypeNeverValidGenericArgument() at:
     // https://github.com/dotnet/runtime/blob/4f5c6938d09e935830492c006aa8381611b65ad8/src/libraries/System.Private.CoreLib/src/System/RuntimeType.cs#L736
-    private static bool IsInvalidType(Type type) {
-        return  type.IsPointer || type.IsByRef || type == typeof(void) ||
-                type.IsByRefLike; // type is a ref struct. E.g. Span<>
+private static bool IsInvalidType(Type type)
+{
+    if (type.IsPointer || type.IsByRef || type == typeof(void))
+        return true;
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+    if (type.IsByRef)
+        return true;
+    if (type.IsGenericType)
+    {
+        var genericTypeDef = type.GetGenericTypeDefinition();
+        if (genericTypeDef == typeof(Span<>) || genericTypeDef == typeof(ReadOnlySpan<>))
+            return true;
     }
+    return false;
+#else
+    return type.IsByRefLike; // type is a ref struct. E.g. Span<>
+#endif
+}
     
     // ReSharper disable UnusedMember.Local
     [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026", Justification = "Not called for NativeAOT")]
diff --git a/src/ECS/Friflo.Engine.ECS.csproj b/src/ECS/Friflo.Engine.ECS.csproj
index 1fd4ceb4..fa5b2068 100644
--- a/src/ECS/Friflo.Engine.ECS.csproj
+++ b/src/ECS/Friflo.Engine.ECS.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>library</OutputType>
-    <TargetFrameworks>net8.0;net7.0;net6.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>net8.0;net7.0;net6.0;netstandard2.1;netstandard2.0</TargetFrameworks>
     <ImplicitUsings>disable</ImplicitUsings>
     <Nullable>disable</Nullable>
     <RootNamespace>Friflo.Engine.ECS</RootNamespace>
diff --git a/src/ECS/Systems/Extensions/SystemPerf.cs b/src/ECS/Systems/Extensions/SystemPerf.cs
index e5db3d5c..20e84300 100644
--- a/src/ECS/Systems/Extensions/SystemPerf.cs
+++ b/src/ECS/Systems/Extensions/SystemPerf.cs
@@ -92,7 +92,11 @@ public PerfResource () {
     
     [ExcludeFromCodeCoverage]
     internal static long GetAllocatedBytes() {
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+        return 0; 
+#else
         return Platform.IsUnityRuntime ? 0 : GC.GetAllocatedBytesForCurrentThread(); 
+#endif
     }
 }
 
diff --git a/src/ECS/Utils/TreeUtils.cs b/src/ECS/Utils/TreeUtils.cs
index fa94f27a..27d292f4 100644
--- a/src/ECS/Utils/TreeUtils.cs
+++ b/src/ECS/Utils/TreeUtils.cs
@@ -80,7 +80,12 @@ private static void DuplicateChildren(Entity entity, Entity clone, EntityStore s
     public static AddDataEntitiesResult AddDataEntitiesToEntity(Entity targetEntity, IReadOnlyList<DataEntity> dataEntities)
     {
         var entityCount     = dataEntities.Count;
+#if NETSTANDARD && !NETSTANDARD2_1_OR_GREATER
+        var childEntities   = new HashSet<long>         ();
+        childEntities.EnsureCapacity(entityCount);
+#else
         var childEntities   = new HashSet<long>         (entityCount);
+#endif
         var oldToNewPid     = new Dictionary<long, long>(entityCount);
         var newToOldPid     = new Dictionary<long, long>(entityCount);
         var store           = targetEntity.Store;
diff --git a/src/Hub/Engine.Hub.csproj b/src/Hub/Engine.Hub.csproj
index e772da1c..a61ccf6f 100644
--- a/src/Hub/Engine.Hub.csproj
+++ b/src/Hub/Engine.Hub.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>library</OutputType>
-    <TargetFrameworks>net8.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>net8.0;netstandard2.1;netstandard2.0</TargetFrameworks>
     <ImplicitUsings>disable</ImplicitUsings>
     <Nullable>disable</Nullable>
     <RootNamespace>Friflo.Engine.Hub</RootNamespace>
diff --git a/src/Tests-NativeAOT/Tests-NativeAOT.csproj b/src/Tests-NativeAOT/Tests-NativeAOT.csproj
index a856e958..6f94e6d5 100644
--- a/src/Tests-NativeAOT/Tests-NativeAOT.csproj
+++ b/src/Tests-NativeAOT/Tests-NativeAOT.csproj
@@ -2,7 +2,6 @@
 
     <PropertyGroup>
         <OutputType>Exe</OutputType>
-        <PublishAot>true</PublishAot>
         <!-- <DefineConstants Condition="'$(PublishAot)' == 'true'">
             $(DefineConstants);IS_NATIVE_AOT
         </DefineConstants> -->