The 2002 World War II-themed FPS launched a franchise that, between games and DLC, has had more than 20 releases in the last ten years. In honor of reaching that 10th anniversary, EA is making Battlefield 1942 available as a free download via their Origin service. The download includes the base game only, with no expansions. EA's FAQ says that mod support is "untested," but advises players where to go to talk through mod support on their own.
10th Anniversary: Download and play Battlefield 1942 for free! [Battlefield blog]