Unreal Tournament (opens in new tab), as in the 1999 multiplayer first-person-shooter, has been demade for a new platform—the Atari VCS, aka the Atari 2600, a 41-year-old console. Fortunately you don't need to have kept your Atari since 1977 to play it, as UT 2600 runs in an emulator or can be enjoyed right in your browser.
This bleepy, chunky, 2D version of Unreal Tournament features capture-the-flag and deathmatch modes, can be played with a friend locally or online, and includes various classic pickups and weapons like everyone's favorite gun, the flak cannon (opens in new tab).
UT 2600 is still in beta at the moment, but there are plans for a physical cartridge release in the future. In the meantime, check it out here (opens in new tab).