Open Transport Tycoon Deluxe, or OpenTTD, is an open-source transport network management game based on the 1995 MicroProse release Transport Tycoon Deluxe. It mimics the original game closely but adds a significant number of new features and general improvements. OpenTTD began as a mod for the original game, but became its own stand-alone open source community driven game on April 1st, 2010 after a long-term community effort to divorce OpenTTD from the base game's proprietary assets. This resulted in the stand-alone release using community created open source graphics and music, and no longer requires the user to have a physical copy of the game to run it. OpenTTD also added multiplayer which has proven especially popular and has greatly contributed to the game's continued following well after release.
OpenTTD added many smaller, but still significant features that have kept the game relatively accessible to new players while also making it possible to create transportation networks that are more complex than would have been feasible in the 1995 release. Additionally, an in-game mod browser means that the many mods created by the OpenTTD community can be installed through the game client.