Revenge Of The Cats: Ethernet is a fast-paced, moddable, freeware, multiplayer first-person shooter:
Players start out in Etherform and need to find a zone owned by their team in order to manifest as a CAT. As CAT, players take zones for their team simply by being inside the zone while no enemy CAT is also present in the zone. The zone then turns red or blue, depending on which team captured it. If CATs of both teams are present, the zone remains white.
Here’s some footage a reader (thanks Vann) pointed out: