Indie games are distinct from open source games. The latter are games which are developed with the intent to release the source code and other assets under an open source license. While many of the same principles used to develop open source games are the same as for indie games, open source games are not developed for commercial gain and instead as a hobbyist pursuit. However, commercial sales are not a requirement for an indie game and such games can be offered as freeware, most notably with "Spelunky" on its original release and "Dwarf Fortress" with exception of a planned enhanced visual front-end version while its base version will remain free.