diff --git a/src/Immersion/Program.cs b/src/Immersion/Program.cs
index 18caa82..e28acfa 100644
--- a/src/Immersion/Program.cs
+++ b/src/Immersion/Program.cs
@@ -20,9 +20,10 @@ FlecsAbortException.SetupHook();
 Resources.ResourceAssembly = typeof(Program).Assembly;
 
 var universe = new Universe();
-var game     = universe.LookupOrThrow<Game>();
-universe.EnableRest();
-universe.EnableMonitor();
+var game = universe.LookupOrThrow<Game>();
+
+universe.Modules.Register<gaemstone.Systems.Rest>();
+universe.Modules.Register<gaemstone.Systems.Monitor>();
 
 var window = Window.Create(WindowOptions.Default with {
 	Title = "gæmstone",
diff --git a/src/gaemstone/ECS/Universe+Modules.cs b/src/gaemstone/ECS/Universe+Modules.cs
index 39acdf7..01edca4 100644
--- a/src/gaemstone/ECS/Universe+Modules.cs
+++ b/src/gaemstone/ECS/Universe+Modules.cs
@@ -45,12 +45,9 @@ public class ModuleManager
 
 			foreach (var nested in type.GetNestedTypes()) {
 				if (nested.Get<EntityAttribute>() is not EntityAttribute nestedAttr) continue;
-
-				var name = nestedAttr.Name ?? nested.Name;
-				if (name.Contains('.')) throw new Exception(
+				if (nestedAttr.Name?.Contains('.') == true) throw new Exception(
 					$"EntityAttribute.Name for {type} must not contain a dot (path separator)");
-
-				Universe.LookupOrThrow($"{moduleName}.{name}")
+				Universe.LookupOrThrow($"{moduleName}.{nestedAttr.Name ?? nested.Name}")
 					.CreateLookup(nested);
 			}
 
@@ -58,14 +55,10 @@ public class ModuleManager
 
 		} else {
 
-			var name = GetModuleName(type);
-			if (Universe.Lookup(name) != null) throw new Exception(
-				$"Can't register module {type}: '{type.FullName}' is already in use");
-
+			var name   = GetModuleName(type);
 			var module = new ModuleInfo(Universe, type, name);
 			_modules.Add(module.Entity, module);
 			TryEnableModule(module);
-
 			return module.Entity;
 
 		}
diff --git a/src/gaemstone/ECS/Universe.cs b/src/gaemstone/ECS/Universe.cs
index c211e73..663655b 100644
--- a/src/gaemstone/ECS/Universe.cs
+++ b/src/gaemstone/ECS/Universe.cs
@@ -1,5 +1,4 @@
 using System;
-using System.Runtime.InteropServices;
 using static flecs_hub.flecs;
 using static flecs_hub.flecs.Runtime;
 
@@ -29,29 +28,6 @@ public unsafe partial class Universe
 	public EntityBuilder New(string? name = null, string? symbol = null)
 		=> new(this, name, symbol);
 
-	// TODO: Move to module.
-	public void EnableRest(ushort port = 27750)
-	{
-		[UnmanagedCallersOnly]
-		static void RestImport(ecs_world_t* world)
-			=> FlecsRestImport(world);
-
-		ecs_import_c(this, new() { Data = new() { Pointer = &RestImport } }, "FlecsRest");
-
-		var rest = LookupOrThrow("flecs.rest.Rest");
-		_lookupByType.Add(typeof(EcsRest), rest);
-		rest.Set(new EcsRest { port = port });
-	}
-
-	public void EnableMonitor()
-	{
-		[UnmanagedCallersOnly]
-		static void MonitorImport(ecs_world_t* world)
-			=> FlecsMonitorImport(world);
-
-		ecs_import_c(this, new() { Data = new() { Pointer = &MonitorImport } }, "FlecsMonitor");
-	}
-
 	public bool Progress(TimeSpan delta)
 		=> ecs_progress(this, (float)delta.TotalSeconds);
 
diff --git a/src/gaemstone/Systems/Monitor.cs b/src/gaemstone/Systems/Monitor.cs
new file mode 100644
index 0000000..52fa273
--- /dev/null
+++ b/src/gaemstone/Systems/Monitor.cs
@@ -0,0 +1,20 @@
+using System.Runtime.InteropServices;
+using gaemstone.ECS;
+using static flecs_hub.flecs;
+
+namespace gaemstone.Systems;
+
+[Module(Name = "flecs.monitor")]
+public unsafe class Monitor
+	: IModuleInitializer
+{
+	public void Initialize(EntityRef entity)
+	{
+		ecs_import_c(entity.Universe, new() { Data = new() {
+			Pointer = &MonitorImport } }, "FlecsMonitor");
+	}
+
+	[UnmanagedCallersOnly]
+	private static void MonitorImport(ecs_world_t* world)
+		=> FlecsMonitorImport(world);
+}
diff --git a/src/gaemstone/Systems/Rest.cs b/src/gaemstone/Systems/Rest.cs
new file mode 100644
index 0000000..8d156d3
--- /dev/null
+++ b/src/gaemstone/Systems/Rest.cs
@@ -0,0 +1,22 @@
+using System.Runtime.InteropServices;
+using gaemstone.ECS;
+using static flecs_hub.flecs;
+
+namespace gaemstone.Systems;
+
+[Module(Name = "flecs.rest")]
+public unsafe class Rest
+	: IModuleInitializer
+{
+	public void Initialize(EntityRef entity)
+	{
+		ecs_import_c(entity.Universe, new() { Data = new() {
+			Pointer = &RestImport } }, "FlecsRest");
+		entity.NewChild("Rest").Build()
+			.CreateLookup<EcsRest>().Set(new EcsRest { port = 27750 });
+	}
+
+	[UnmanagedCallersOnly]
+	static void RestImport(ecs_world_t* world)
+		=> FlecsRestImport(world);
+}