Where’s the commander keen?
Back in 2014 John Hall found the source to some of the old stuff, including Keen 4,5,6
https://games.slashdot.org/story/14/09/17/133228/commander-k...
The game was bought by fans, the source was released and Keen Dreams was published on steam.
https://github.com/keendreams/keen
https://store.steampowered.com/app/356200/Keen_Dreams/
The ownership of the older stuff is quite fragmented.