I run a couple of unpopular servers for games that I'm interested in.
QUAKE II DM, Bots, Chaos
A few Quake II servers. Easiest way to run Quake II these days is either run it from Steam, or download the Q2Pro Enhanced Client from http://q2s.tastyspleen.net. It's excellent old school fun / nostalgia-fest. I'd forgotten how nuts Chaos Q2 DM was with happy mines and the portal thing. I'll try to keep them running in case anyone ever fancies playing Q2.