Vendetta Online (VO) is a twitch-based, science fiction massively multiplayer online role-playing game (MMORPG) developed by Guild Software for the operating systems Android, Linux, Mac OS X, iOS, and Microsoft Windows. It uses the NAOS game engine, a fully realtime flight model and combat system, that brings the intensity and immersion of first person/third person shooter-style PvP and PvNPC battle action, set against the backdrop of a massively multiplayer universe. Vendetta Online shipped as a commercial MMORPG on November 1, 2004 with a subscription-based business model, although it has been running continuously since April 2002. Vendetta Online is available to play across a wide array of platforms, allowing all users to directly interact in a single, contiguous galaxy. It is also notable for its twitch combat and fidelity to real physics. It is updated regularly with new content and bugfixes.