Halo: Custom Edition, sometimes abbreviated Halo CE, is a free stand-alone expansion for Halo Combat Evolved by Bungie Studios, which was ported to the PC by Gearbox Software. Halo CE was released by Gearbox as an unsupported add-on, which requires the original game. To prevent confusion between Halo Custom Edition and Halo: Combat Evolved (which can both be expressed as Halo CE) the original version of Halo (Combat Evolved) is referred to as Halo PC.