Ventrilo. It's a voice communication channel. I have a spare one I'm not using that I might be convinced to let people use if there's enough interest.
Ventrilo is sort of like a multi-user "audio chat room", so to speak. Skype is for one-to-one communication (if I am not mistaken).
It's very low-resource program that gives very, very clear audio to large groups of people. That way, all the people on ST:O could talk to each other almost as clearly as if they were on the phone. I'll post a quick vid soon showing my linkshell in ventrilo chat.
Here we go: http://s19.photobucket.com/albums/b186/Talkahuano/?action=view¤t=ventrilo_0001.flv The video shows a small handful of people, but we've had 30+ no problem. You can also be split into different rooms, so there can be multiple chat groups on at the same time. My linkshell typically uses the FFXI and AFK rooms, but you can see they have lots of rooms for WoW and a few other things.
Skype can host multi-user rooms and is generally better quality than vent servers. However, skype gets hosted on the machine of one user in the chat, which is both good and bad. It's good because you don't need to pay for a server. It's bad because it can clog up that persons connection and can't support as many users. Ventrilo was designed for use in games and as such is designed to host multiple rooms and many users. It also supports push-to-talk (use a hotkey to activate your voice transmission), where as skype just transmits everything all the time (since it is designed for a phone call). It can be annoying to play games over skype due to sounds of peoples keyboards, speakers, background noise, etc. When you have many users, this random background noise will pretty much ruin the usability of the service. I prefer using skype when I play games or chat with 3-4 friends. But if you are hosting a chat with 8+ people, skype doesn't work so well.
