A new free-to-play Halo game has just been announced, and it's heading exclusively to Russia. A collaboration between 343 Industries, Saber Interactive and Innova Systems, Halo Online is set to launch this spring. The game will be powered by a modified version of the Halo 3 game engine. There's no solo campaign, and the game will be set on a secret UNSC space installation called Anvil where Spartans are on hand to shoot each other repeatedly with bug guns, presumably.
The closed beta is due to start in spring, and there's currently no plans to take the game to other territories, "theoretically" it's possible although "any expansion outside of Russia would have to go through region-specific changes to address player expectations." If you want to find out more there's a short Q&A on Halo Waypoint.