Duality is a plugin-based 2Dgame development framework based on C# and OpenTK. To get a quick overview, please visit the project page. Duality is a modular 2Dgame engine that provides its own visual editor. It's highly extensible, written entirely in C# and backed by OpenGL. For a lot of game libraries, your code has the active role of setting everything up and managing it.
All-in-one program for creating 2D scrolling games. Compile your games into stand-alone .NET executables or customizable C# source code. The IDE and framework are build on OpenTK, which wraps OpenGL, so generated games can be cross-platform.
Ever wanted to use a Wii Remote, pheraps a Multitouch surface or the Microsoft Kinect to control your application/game even if web based? If so, then MonoMIG (Multi Input Gateway) is what you are looking for!
Hotaru is an XNA-based Game Engine that is intended to be used for 2D Action RPGs. Game Developers can use Tonbo (a Visual Studio Plug-in) to create and distribute games that run on Hotaru.
BooGame is an object oriented CLS-compliant, 2Dgame engine framework that provides high-level hardware accelerated video, audio, keyboard, mouse, embedded scripting and many image formats. Written in C#, BooGame targets .NET 1.1, 2.0 and Mono platforms.