Utterly Mad

You can download all of them for free, with an pre-optimized DOSbox setup included. I posted a link in this very thread a while back.

Honestly though, having put literally thousands of hours into the series, I'd suggest getting Xenonauts. It does away with the worst aspects of the original series and keeps the majority of the good stuff. Also, tons of mods these days, some of which are actually decent.

I'd also really suggest that if you must try the originals (which, as much as I hate to admit it, haven't aged very well), use the link and don't waste money on Steam. The Steam versions don't work without putting in some effort.

http://gamesnostalgia.com/en/

Games. Free games. That actually work. I don't know how I never found that place before, but fuck yeah.

There it is. They have everything from MoO2 to Syndicate to the Red Baron to X-Com, and they are pretty much all playing ready. Pretty much the games of my youth.