The main description will fit in some kind of live chat support system. However, there are some big differences and advantages:
- You can open a chat window (inline or pop-up) to any online visitor.
- Run on multiple sites: one master centralized site and many clients (domains) to serve.
- Optimized for high traffic sites.
- Client sites just need add a small javascript, no php involved.
- Only open connections when some status change (admin logged, new chat, etc).
- Chat's script is really fast using filesystem for writing.
- Idem for reading, just show file contents via ajax.
- Show your online status.
- Log chat messages.