CryBits is a completely open-source 2D ORPG game engine written in C#.
Pull requests are very welcome. You can check the project roadmap page to check the planned resources to try to implement them. For other changes, please open an issue first to discuss what you would like to change. Bug fixes are always welcome too.
For help you can access the official project page, start a discussion or even send me an email, I am always able to help!