This is my pet-project right now. It's basically going to be a casual head-to-head dogfight game. The motivation for me is to try out C# as a game programming language, specifically in combination with OpenTK.
I've built this game in 2d yearlier - Amiga/AMOS several years ago, c/allegro/dos and C#/Windows.Forms - but never in 3d. The idea is to keep the game mechanics in 2d, while rendering everything in 3d. I will stay at the "solid color polygon" level, no textures, to get the right retro feeling.
If you try it out, beware it's like version 0.01 meaning you may control one of the planes using keys A and D, and use Escape to quit, but not much more right now ;)
I'm releasing it under MIT license at Sourceforge if anyone wants to peek under the hood:
Just unzip and copy OpenTK.dll into it to try it out!