The "Halo" series of games is made by Microsoft and 343 Industries as of 2015. Bungie Inc., the original developer of the game, was purchased by Microsoft in 2000.
The original "Halo" series was developed by Bungie Inc. and was supposed to be a trilogy for both the Mac and PC. When Bungie was purchased by Microsoft in 2000, "Halo" became an Xbox-exclusive title. Bungie eventually split off from Microsoft but still developed "Halo: Reach" and "Halo 3: ODST" even though Microsoft still retained the rights to the series. Microsoft created 343 Industries solely to handle the "Halo" franchise. As of April 2015, there have been 10 different "Halo" games released.