“I came across this at a very sad point in my life, it was on a hard drive on a vintage computer I bought off Amazon,” Marshall explains on the expansion’s GitHub page. “Literally this essentially saved my life, I was going through a divorce and just happen[ing] to come across something like this was insane.”
‘Xenonauts’ is probably your best bet, since it’s said to be faithful to the original games and received very good reviews.