diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index d07e46a..df679e7 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -15,33 +15,33 @@ jobs:
         with:
           path: ${{ github.event.repository.name }}
             
-      - name: Checkout `worlds`
+      - name: Checkout `types`
         uses: actions/checkout@v4.1.2
         with:
-          repository: simulation-tree/worlds
+          repository: simulation-tree/types
           token: ${{ secrets.PAT }}
-          path: worlds
+          path: types
       
-      - name: Checkout `types`
+      - name: Checkout `collections`
         uses: actions/checkout@v4.1.2
         with:
-          repository: simulation-tree/types
+          repository: simulation-tree/collections
           token: ${{ secrets.PAT }}
-          path: types
+          path: collections
       
-      - name: Checkout `unmanaged`
+      - name: Checkout `worlds`
         uses: actions/checkout@v4.1.2
         with:
-          repository: simulation-tree/unmanaged
+          repository: simulation-tree/worlds
           token: ${{ secrets.PAT }}
-          path: unmanaged
+          path: worlds
       
-      - name: Checkout `collections`
+      - name: Checkout `unmanaged`
         uses: actions/checkout@v4.1.2
         with:
-          repository: simulation-tree/collections
+          repository: simulation-tree/unmanaged
           token: ${{ secrets.PAT }}
-          path: collections
+          path: unmanaged
             
       - name: Setup
         uses: actions/setup-dotnet@v4
@@ -51,15 +51,27 @@ jobs:
       - name: Set VERSION variable from tag
         run: echo "VERSION=${GITHUB_REF/refs\/tags\/v/}" >> $GITHUB_ENV
             
+      - name: Build `Simulation.Core`
+        run: dotnet build "${{ github.event.repository.name }}/core" -c Debug /p:Version=${VERSION}
+      
       - name: Build `Simulation.Core`
         run: dotnet build "${{ github.event.repository.name }}/core" -c Release /p:Version=${VERSION}
       
+      - name: Build `Simulation.Generator`
+        run: dotnet build "${{ github.event.repository.name }}/generator" -c Debug /p:Version=${VERSION}
+      
       - name: Build `Simulation.Generator`
         run: dotnet build "${{ github.event.repository.name }}/generator" -c Release /p:Version=${VERSION}
       
+      - name: Build `Simulation`
+        run: dotnet build "${{ github.event.repository.name }}/source" -c Debug /p:Version=${VERSION}
+      
       - name: Build `Simulation`
         run: dotnet build "${{ github.event.repository.name }}/source" -c Release /p:Version=${VERSION}
       
+      - name: Build `Simulation.Tests`
+        run: dotnet build "${{ github.event.repository.name }}/tests" -c Debug /p:Version=${VERSION}
+      
       - name: Build `Simulation.Tests`
         run: dotnet build "${{ github.event.repository.name }}/tests" -c Release /p:Version=${VERSION}
             
@@ -67,13 +79,13 @@ jobs:
         run: dotnet test "${{ github.event.repository.name }}/tests" -c Release --logger "trx"
             
       - name: Pack `Simulation.Core`
-        run: dotnet pack "${{ github.event.repository.name }}/core" -c Release /p:Version=${VERSION} --no-build --output .
+        run: dotnet pack "${{ github.event.repository.name }}/core" /p:Version=${VERSION} --no-build --output .
       
       - name: Pack `Simulation.Generator`
-        run: dotnet pack "${{ github.event.repository.name }}/generator" -c Release /p:Version=${VERSION} --no-build --output .
+        run: dotnet pack "${{ github.event.repository.name }}/generator" /p:Version=${VERSION} --no-build --output .
       
       - name: Pack `Simulation`
-        run: dotnet pack "${{ github.event.repository.name }}/source" -c Release /p:Version=${VERSION} --no-build --output .
+        run: dotnet pack "${{ github.event.repository.name }}/source" /p:Version=${VERSION} --no-build --output .
 
       - name: Add NuGet Source
         run: dotnet nuget add source https://nuget.pkg.github.com/${{ github.repository_owner }}/index.json --name github --username ${{ github.repository_owner }} --password ${{ github.token }} --store-password-in-clear-text
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index be0882a..9a53745 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -28,33 +28,33 @@ jobs:
         with:
           path: ${{ github.event.repository.name }}
             
-      - name: Checkout `worlds`
+      - name: Checkout `types`
         uses: actions/checkout@v4.1.2
         with:
-          repository: simulation-tree/worlds
+          repository: simulation-tree/types
           token: ${{ secrets.PAT }}
-          path: worlds
+          path: types
       
-      - name: Checkout `types`
+      - name: Checkout `collections`
         uses: actions/checkout@v4.1.2
         with:
-          repository: simulation-tree/types
+          repository: simulation-tree/collections
           token: ${{ secrets.PAT }}
-          path: types
+          path: collections
       
-      - name: Checkout `unmanaged`
+      - name: Checkout `worlds`
         uses: actions/checkout@v4.1.2
         with:
-          repository: simulation-tree/unmanaged
+          repository: simulation-tree/worlds
           token: ${{ secrets.PAT }}
-          path: unmanaged
+          path: worlds
       
-      - name: Checkout `collections`
+      - name: Checkout `unmanaged`
         uses: actions/checkout@v4.1.2
         with:
-          repository: simulation-tree/collections
+          repository: simulation-tree/unmanaged
           token: ${{ secrets.PAT }}
-          path: collections
+          path: unmanaged
             
       - name: Setup
         uses: actions/setup-dotnet@v4
diff --git a/core/Simulation.Core.csproj b/core/Simulation.Core.csproj
index ce2db7f..b375133 100644
--- a/core/Simulation.Core.csproj
+++ b/core/Simulation.Core.csproj
@@ -1,35 +1,41 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
-	<PropertyGroup>
-		<TargetFramework>net9.0</TargetFramework>
-		<ImplicitUsings>disable</ImplicitUsings>
-		<Nullable>enable</Nullable>
-		<AllowUnsafeBlocks>True</AllowUnsafeBlocks>
-		<IsAotCompatible>True</IsAotCompatible>
-		<IsTrimmable>True</IsTrimmable>
-		<TreatWarningsAsErrors>True</TreatWarningsAsErrors>
-		<Authors>popcron</Authors>
-		<Company>simulation-tree</Company>
-		<Description>Logic upon data</Description>
-		<RepositoryUrl>https://github.com/simulation-tree/simulation</RepositoryUrl>
-		<PackageReadmeFile>README.md</PackageReadmeFile>
-		<PackageTags>ecs</PackageTags>
-		<Title>Simulation Core</Title>
-		<RootNamespace>Simulation</RootNamespace>
-		<PackageId />
-		<GenerateDocumentationFile>True</GenerateDocumentationFile>
-	</PropertyGroup>
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <ImplicitUsings>disable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+    <IsAotCompatible>True</IsAotCompatible>
+    <IsTrimmable>True</IsTrimmable>
+    <TreatWarningsAsErrors>True</TreatWarningsAsErrors>
+    <Authors>popcron</Authors>
+    <Company>simulation-tree</Company>
+    <Description>Logic upon data</Description>
+    <RepositoryUrl>https://github.com/simulation-tree/simulation</RepositoryUrl>
+    <PackageReadmeFile>README.md</PackageReadmeFile>
+    <PackageTags>ecs</PackageTags>
+    <Title>Simulation Core</Title>
+    <RootNamespace>Simulation</RootNamespace>
+    <GenerateDocumentationFile>True</GenerateDocumentationFile>
+    <IncludeBuildOutput>false</IncludeBuildOutput>
+    <OutDir>bin/$(TargetFramework)/$(Configuration)</OutDir>
+  </PropertyGroup>
 
-	<ItemGroup>
-		<None Include="..\README.md">
-			<Pack>True</Pack>
-			<PackagePath>\</PackagePath>
-		</None>
-	</ItemGroup>
+  <ItemGroup>
+    <None Include="..\README.md">
+      <Pack>True</Pack>
+      <PackagePath>\</PackagePath>
+    </None>
+  </ItemGroup>
 
-	<ItemGroup>
-		<ProjectReference Include="..\..\collections\source\Collections.csproj" />
-		<ProjectReference Include="..\..\types\core\Types.Core.csproj" />
-	</ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\collections\source\Collections.csproj"/>
+    <ProjectReference Include="..\..\types\core\Types.Core.csproj"/>
+  </ItemGroup>
+
+  <ItemGroup>
+    <Content Include="bin/**/*" Pack="true" PackagePath="lib" Visible="false"/>
+    <Content Include="buildTransitive/**/*" Pack="true" PackagePath="buildTransitive"/>
+  </ItemGroup>
 
 </Project>
\ No newline at end of file
diff --git a/core/SystemGroup.cs b/core/SystemGroup.cs
new file mode 100644
index 0000000..0066410
--- /dev/null
+++ b/core/SystemGroup.cs
@@ -0,0 +1,152 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Threading;
+
+namespace Simulation
+{
+    /// <summary>
+    /// A group of systems that all run on a separate foreground thread.
+    /// </summary>
+    public sealed class SystemGroup<T> : IDisposable, IListener<T> where T : unmanaged
+    {
+        private readonly CancellationTokenSource cts;
+        private readonly Thread thread;
+        private IListener<T>[] systems;
+        private bool disposed;
+        private volatile int messageVersion;
+        private volatile bool finishedSignal;
+        private T message;
+
+        int IListener.Count => 1;
+
+        /// <summary>
+        /// Creates a new system group.
+        /// </summary>
+        public SystemGroup(ReadOnlySpan<char> threadName)
+        {
+            systems = [];
+            cts = new();
+            thread = new Thread(Run);
+            thread.Name = threadName.ToString();
+            thread.IsBackground = false;
+            thread.Start();
+        }
+
+        void IListener.CollectMessageHandlers(Span<MessageHandler> messageHandlers)
+        {
+            messageHandlers[0] = MessageHandler.Get<IListener<T>, T>(this);
+        }
+
+        private void Run()
+        {
+            SpinWait waiter = new();
+            int lastMessageVersion = 0;
+            while (true)
+            {
+                while (lastMessageVersion == messageVersion && !cts.IsCancellationRequested)
+                {
+                    waiter.SpinOnce();
+                }
+
+                if (cts.IsCancellationRequested)
+                {
+                    break;
+                }
+
+                Thread.MemoryBarrier();
+                T currentMessage = message;
+                lastMessageVersion = messageVersion;
+
+                foreach (IListener<T> system in systems)
+                {
+                    system.Receive(ref currentMessage);
+                }
+
+                waiter.Reset();
+                finishedSignal = true;
+            }
+        }
+
+        /// <summary>
+        /// Disposes the system group and finishes work on its thread.
+        /// </summary>
+        public void Dispose()
+        {
+            ThrowIfDisposed();
+
+            disposed = true;
+            cts.Cancel();
+            if (thread.IsAlive)
+            {
+                thread.Join();
+            }
+
+            cts.Dispose();
+        }
+
+        /// <summary>
+        /// Adds the given <paramref name="system"/> to the group.
+        /// </summary>
+        public void Add<S>(S system) where S : IListener<T>
+        {
+            ThrowIfDisposed();
+
+            Array.Resize(ref systems, systems.Length + 1);
+            systems[^1] = system;
+        }
+
+        /// <summary>
+        /// Removes the system of type <typeparamref name="S"/> from the group.
+        /// </summary>
+        public void Remove<S>() where S : IListener<T>
+        {
+            ThrowIfDisposed();
+
+            List<IListener<T>> systemList = new(systems);
+            for (int i = 0; i < systemList.Count; i++)
+            {
+                if (systemList[i] is S system)
+                {
+                    systemList.RemoveAt(i);
+                    if (system is IDisposable disposable)
+                    {
+                        disposable.Dispose();
+                    }
+
+                    break;
+                }
+            }
+
+            systems = systemList.ToArray();
+        }
+
+        /// <summary>
+        /// Signals the thread to process the given <paramref name="message"/>.
+        /// </summary>
+        public void Receive(ref T message)
+        {
+            ThrowIfDisposed();
+
+            finishedSignal = false;
+            this.message = message;
+            Thread.MemoryBarrier();
+            Interlocked.Increment(ref messageVersion);
+
+            SpinWait waiter = new();
+            while (!finishedSignal)
+            {
+                waiter.SpinOnce();
+            }
+        }
+
+        [Conditional("DEBUG")]
+        private void ThrowIfDisposed()
+        {
+            if (disposed)
+            {
+                throw new ObjectDisposedException(nameof(SystemGroup<T>), "This system group has already been disposed");
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/core/buildTransitive/Simulation.Core.targets b/core/buildTransitive/Simulation.Core.targets
new file mode 100644
index 0000000..64a0488
--- /dev/null
+++ b/core/buildTransitive/Simulation.Core.targets
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+    <ItemGroup>
+        <Reference Include="Simulation.Core">
+            <HintPath>$(MSBuildThisFileDirectory)..\lib\net9.0\$(Configuration)\Simulation.Core.dll</HintPath>
+        </Reference>
+    </ItemGroup>
+
+</Project>
\ No newline at end of file
diff --git a/tests/MultithreadedTests.cs b/tests/MultithreadedTests.cs
new file mode 100644
index 0000000..4d9252e
--- /dev/null
+++ b/tests/MultithreadedTests.cs
@@ -0,0 +1,36 @@
+namespace Simulation.Tests
+{
+    public class MultithreadedTests : SimulationTests
+    {
+        [Test]
+        public void SystemGroupCreation()
+        {
+            SystemGroup<UpdateMessage> group = new("update group");
+            TimeSystem a = new();
+            group.Add(a);
+            Simulator.Add(group);
+            Simulator.Broadcast(new UpdateMessage(0.1));
+            Assert.That(a.time, Is.EqualTo(0.1));
+            Simulator.Remove(group);
+            Simulator.Broadcast(new UpdateMessage(0.1));
+            Assert.That(a.time, Is.EqualTo(0.1));
+            group.Dispose();
+        }
+
+        [Test]
+        public void MultipleSystems()
+        {
+            SystemGroup<UpdateMessage> group = new("update group");
+            TimeSystem a = new();
+            TimeSystem b = new();
+            group.Add(a);
+            group.Add(b);
+            Simulator.Add(group);
+            Simulator.Broadcast(new UpdateMessage(0.1));
+            Assert.That(a.time, Is.EqualTo(0.1));
+            Assert.That(b.time, Is.EqualTo(0.1));
+            Simulator.Remove(group);
+            group.Dispose();
+        }
+    }
+}
\ No newline at end of file