Downloading Old Versions of KSP
Some pretty old versions of KSP were available before on the KSP main site, but by some reason beyound me, it's some time since the links were dropped.
Well, some smart SAS :P made mirrors on Archive. Enjoy it!
Unfortunately, only Windows versions are available - no Linux or Mac.
If you know of something, please contact me.
The source of this information is this post on Forum and were working as 2020-0725 except by the 0.18.3, currently dead.