What made OpenTTD a great success that it's playable out of the box. Most open source game remakes [0] are engine-only and you still need the graphics, arts, sound, and music assets to make it a 100%, and actual playable experience. OpenTTD started like that too but from the very beginning it was a goal to "detach" the game from the original as quickly as possible. It was released in 2004, the actual graphics replacement project started in 2007 and by 2009 100% of the sprites were finished so the original game files were not needed anymore [1]
And actually there are now 5 different basesets on top of the original TTD one [2]
It also made possible things like releasing the game on Steam and GOG.
0, https://github.com/radek-sprta/awesome-game-remakes
1, https://wiki.openttd.org/en/Archive/Community/Graphics%20Rep...
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