Return to the Roots is an open source recreation of The Settlers 2 Gold
Edition game engine. You need the original game assets though to play
the game. (available on https://www.gog.com)

After buying the GOG version of Settlers 2, you can play Return to the
Roots with the following steps:

$ cd /opt/returntotheroots/share/s25rttr/S2
$ innoextract /path/to/my/setup_the_settlers_2_gold_*.exe
$ returntotheroots