more related

README.md

@@ -323,7 +323,11 @@ This project can be used to manage cyclic data structures with memory safe.
 
 See https://github.com/hsutter/gcpp and its video from cppcon 2016 [Leak Freedom in C++... by Default](https://www.youtube.com/watch?v=JfmTagWcqoE).
 
-Other related project is sgcl/tracked_ptr: https://github.com/pebal/sgcl
+Other related projects are:
+
+- sgcl/tracked_ptr: https://github.com/pebal/sgcl
+- https://github.com/nahratzah/cycle_ptr
+- https://github.com/cschreib/observable_unique_ptr
 
 ## Acknowledgements