ShmupNA is a open source game engine for PC/360 using the XNA framework. This engine is tailored to 2d top down arcade style shooters. Currently in the Program Planning stage.
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.