Stride (formerly Xenko), a free and open-source cross-platform C# game
Cross-platform 2D game engine focused on ultimate productivity
Accuracy-focused XNA4 reimplementation for open platforms
Fishstrap is a Bloxstrap Fork.
A Steam library categorizing tool
Modern 3D engine and IDE written using C# and C++.
XNA based game engine completely written in c#
An expanded XNA game creation framework
A lightweight, powerful editing tool for kOS Autopilot Mod on KSP.