Spacewar is a complete starship combat game that comes in two versions: Retro and Evolved. The Retro version is inspired by the first implementation of Spacewar, developed by Stephen Russell, Peter Samson, and Dan Edwards in 1962 for the DEC PDP-1; the Evolved version features similar gameplay, but with 3D models and effects.
The project comes ready to compile and run, and is easy to customize with only a little extra C# programming. The documentation in the starter kit contains a list of some customizations you might make. You're free to use the source code as the basis for your own XNA Game Studio game projects, and to share your work with others.