This document discusses building a game in a day using F# and cross-platform game engines. It provides examples of games that have been created in F# such as a Quake 3 mod and an Xbox Live Arcade game. It also discusses tools for building games in F#, including MonoGame as a successor to XNA. The document concludes with describing a game called The Prismer that was built in 11 hours by a group using F# and tools like Visual Studio and Paint.Net.