It’s freeware on all systems and can be played using ScummVM which has builds for most major platforms - the game files are free to download from ScummVM.org (as well as some other adventure games that have been made freeware like Flight of The Amazon Queen)
This game is free on Linux.
For Ubuntu, just
sudo apt install beneath-a-steel-skyAnd you can start playing.
It’s freeware on all systems and can be played using ScummVM which has builds for most major platforms - the game files are free to download from ScummVM.org (as well as some other adventure games that have been made freeware like Flight of The Amazon Queen)