High Quality Content by WIKIPEDIA articles! 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, and Microsoft Windows. It uses the NAOS game engine, a fully realtime flight model and combat system developed in-house that brings the intensity and immersion of FPS-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. It is updated regularly with new content and bugfixes.