Did it run under DOS? I'm not even asking about a win16 native GUI client. (You can still enjoy CVS if you want to contribute to OpenBSD, for instance.)

Yes, and for Win95 users there was actually a very nice GUI plugin to explorer called TortoiseCVS.

The funny thing about CVS and Subversion is that they were last version control systems that non-programmers could actually use. TortoiseCVS/TortoiseSVN were easy enough that with a lot of training you could get technical writers or artists to use it too. Valuable for game projects. With git, forget about it. It can't even handle binary files well.

Mercurial and TortoiseHg were fine, too.

Only Git had the brain damage to take the source control idea of "there are two areas: working or committed" and add the dumbass index/staging/stash areas that confuse the hell out of everything.

I'm not sure. In the mid-90's, I worked at a Solaris and NT shop, which was where I first used it.