Some of you already know that some of us have been converting XCOM to the Pathfinder RPG system. While that has the advantage of letting you pit your Guild characters against aliens, there are difficulties to the conversion.
I have also been working on just straight converting XCOM into its own pencil-and-paper system.
So here are the Google Docs for people to peruse and enjoy. Of course, they are both works in progress:
XCOM for Pathfinder RPG