Just out of curiosity: Do you know of a good (un)official pen and paper rpg adaptation of the famous first person shooter computer game series Half Life?
I know there are games/systems in which a crafty GM (with a lot of spare time on their hands :)) could recreate the world of Half Life out of scratch, but/so please don't list such unless they have specific, official or unofficial HL "expansions".
(Yes, this question was inspired by the recent release of Beyond Black Mesa, a short fan movie for HL2. Disclaimer: I'm in no way related to said movie.)