Having being an XNA MVP (2009-2013 thanks to my Randomchaos blog on XNA-UK UG) and after MS shut down XNA I got into using Unity, I then started to get back into XNA via MonoGame (thank's for this guys :)) and so, a while ago, started to create my own engine and editor using MonoGame.
The idea being to create an editor for my MonoGame engine that was very similar to Unity. So, at the moment I have scene management, I have a forward and deferred pipeline, I am able to attach C# scripts and run Co-routines like Unity does.
If you want to check out my YouTube clips I have put them here.
Now, I have not looked at my engine for a while, had some life issues crop up (as they always do) but I am now getting back into my engine and it's editor.
I am planning on putting this up on a GitHub repo at some point.