The first one, or the only one that is really playable. It does run great on Linux, except that I did have to change kernel modules to make the VAB usable :^). Listening to L’Impératrice and watching my little green men get stranded on far away moons.

I haven’t played it in a long long time, and I’m both surprised at the amount of muscle memory I’ve retained and the many details that I used to remember too. I used to be able to intuit how much delta-v a mission would need or how much I would have after a complicated staging.