This project is a bit old and no longer maintained. Also some would argue its not a real ECS due to the structure of the components and lack of actual systems. It's still a pretty cool framework, just maybe not what you're looking for.
A 3D Entity-Component-System engine, powered by MonoGame for C# games.
GeonBit docs are available by chapters or as a single file.
In addition, complete API docs can be found online here.
Installing and using GeonBit takes only 3 simple steps!
Some GeonBit demo projects are available here. Feel free to download and use them!
Versions changelog can be found here.