OpenShred
An open source skateboard games engine written in C# and .NET.
A two-tiered project, building a skateboarding games engine on top of a platform abstraction layer and math library called Flake, intended to play a similar role to XNA but designed differently.
The games design is to focus on the feeling of speed and momentum rather than technical details or elaborate tricks.
Built on C#/.NET/Mono with full open source and exporters for Blender, OpenShred is designed to be modified to make it your game too.