diff --git a/src/NATS.Server/Internal/Avl/SequenceSet.cs b/src/NATS.Server/Internal/Avl/SequenceSet.cs
new file mode 100644
index 0000000..5b3c169
--- /dev/null
+++ b/src/NATS.Server/Internal/Avl/SequenceSet.cs
@@ -0,0 +1,7 @@
+namespace NATS.Server.Internal.Avl;
+
+// Go reference: server/avl/seqset.go
+// TODO: Port AVL-backed sparse sequence set
+public class SequenceSet
+{
+}
diff --git a/src/NATS.Server/Internal/Gsl/GenericSubjectList.cs b/src/NATS.Server/Internal/Gsl/GenericSubjectList.cs
new file mode 100644
index 0000000..b2a8cd9
--- /dev/null
+++ b/src/NATS.Server/Internal/Gsl/GenericSubjectList.cs
@@ -0,0 +1,7 @@
+namespace NATS.Server.Internal.Gsl;
+
+// Go reference: server/gsl/gsl.go
+// TODO: Port generic trie-based subject list
+public class GenericSubjectList<T> where T : IEquatable<T>
+{
+}
diff --git a/src/NATS.Server/Internal/SubjectTree/SubjectTree.cs b/src/NATS.Server/Internal/SubjectTree/SubjectTree.cs
new file mode 100644
index 0000000..74a22d5
--- /dev/null
+++ b/src/NATS.Server/Internal/SubjectTree/SubjectTree.cs
@@ -0,0 +1,7 @@
+namespace NATS.Server.Internal.SubjectTree;
+
+// Go reference: server/stree/stree.go
+// TODO: Port Adaptive Radix Tree for per-subject state
+public class SubjectTree<T>
+{
+}
diff --git a/src/NATS.Server/Internal/TimeHashWheel/HashWheel.cs b/src/NATS.Server/Internal/TimeHashWheel/HashWheel.cs
new file mode 100644
index 0000000..00ed916
--- /dev/null
+++ b/src/NATS.Server/Internal/TimeHashWheel/HashWheel.cs
@@ -0,0 +1,7 @@
+namespace NATS.Server.Internal.TimeHashWheel;
+
+// Go reference: server/thw/thw.go
+// TODO: Port time hash wheel for TTL expiration
+public class HashWheel
+{
+}
diff --git a/src/NATS.Server/Raft/IRaftNode.cs b/src/NATS.Server/Raft/IRaftNode.cs
new file mode 100644
index 0000000..00e033d
--- /dev/null
+++ b/src/NATS.Server/Raft/IRaftNode.cs
@@ -0,0 +1,7 @@
+namespace NATS.Server.Raft;
+
+// Go reference: server/raft.go lines 40-92
+// TODO: Port RaftNode interface
+public interface IRaftNode
+{
+}
diff --git a/src/NATS.Server/Raft/RaftState.cs b/src/NATS.Server/Raft/RaftState.cs
new file mode 100644
index 0000000..5c46366
--- /dev/null
+++ b/src/NATS.Server/Raft/RaftState.cs
@@ -0,0 +1,10 @@
+namespace NATS.Server.Raft;
+
+// Go reference: server/raft.go
+public enum RaftState : byte
+{
+    Follower = 0,
+    Leader = 1,
+    Candidate = 2,
+    Closed = 3
+}
diff --git a/tests/NATS.Server.Tests/Concurrency/.gitkeep b/tests/NATS.Server.Tests/Concurrency/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/tests/NATS.Server.Tests/Internal/Avl/.gitkeep b/tests/NATS.Server.Tests/Internal/Avl/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/tests/NATS.Server.Tests/Internal/Gsl/.gitkeep b/tests/NATS.Server.Tests/Internal/Gsl/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/tests/NATS.Server.Tests/Internal/SubjectTree/.gitkeep b/tests/NATS.Server.Tests/Internal/SubjectTree/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/tests/NATS.Server.Tests/Internal/TimeHashWheel/.gitkeep b/tests/NATS.Server.Tests/Internal/TimeHashWheel/.gitkeep
new file mode 100644
index 0000000..e69de29