Bluetooth Chat for MacBook?

Hello,

I'm playing a a few nights at a festival this summer and will be using my macbook with Mainstage 2 for one of my keyboards. I could really do with getting an app for my macbook that would allow me to communicate with the techies (also using a macbook).

Is there an app which has the following features?
- Free, or cheap
- Does NOT require internet for use. (Communicates via bluetooth?)
- Instant Messaging style chat windows- type and hit enter to send immediately.
- No alert sounds OR sounds that can be muted completely.

- Quick

Thanks 🙂