1) Free Trial Edition of 123 Flash Chat
Advantages: It's free but has full functions, even the optional modules including audio and video chat.
Limitation: Only 10 concurrent users may use the room and you need to host it by yourself, which means a dedicated server with SSH access is required.
2) Free Hosting of 123 Flash Chat
Advantages: It's hosted by TOPCMM 123 Flash Chat team, free of charge, no limit to the concurrent user number and provides the basic chat functions.
Limitation: Some management functions are missing.
3) Commercial Server Software or Hosting Service
Advantages: No advertisements, full support service, multiple client choices, etc.