People still play multiplayer, but games aren't too frequent these days. Usually people meet on IRC to chat and occasionally setup games. The network is QuakeNet, the channel is #Outpost2.
There are many IRC clients available. I used to use
mIRC, which is pretty good, but be aware it's nag-ware, and will ask you to either register, or click through an extra box at startup.
There are other IRC clients available, but I'm less familiar with them. Perhaps someone else can give a good suggestion.
The server's list, including QuakeNet, usually comes packaged with the software.