Back when vanilla was the big thing, I had downloaded the game off of a link on a teamspeak server for a C&C Renegade clan, I never played it, and it sat on my hard drive for a long time. I found it and booted it up, this was when RTB 1.045 was current. Still running vanilla, I looked at the server list, filled with servers prefixed with [RTB] and thought it was some giant clan or something. I attempted to join many server, but of course was faced with huge loading times. After I finally figured out what RTB was and downloaded it, the first server I joined was Bleh7777's coaster park.
As far as first retail server, probably Badspot's Block Party (I think it was called that at the time)
I think it was Adam's House of Traps
That was one of the most popular things I hosted; it got a
ton more people than I thought it would.
A friend actually built it and I hosted it for her.