The Fudge RPG site has the rules available for free. You maybe interested in Fate as well which you can get for free. Either would be eminently suitable for modelling a rpg from either a computer game or movie. Both those systems are tool-kits to enhance storytelling more than a model of reality using probabilities. So, if you are looking at a tactical board game with RPG elements set in New Vegas, then I would recommend D&D (or just play Fallout!). If you are looking for a story focused with character developmental (in the literary sense) RPG, then either Fate or Fudge would work well.
Note that neither systems come set up to play either a Fallout, Deus Ex, or Matrix campaigns. You will need to do some work to make them mesh. However, I do not believe it will be much work.