Hydra: Collaborative Text Editor.
I picked this up from my comments on the Social Software post. Hydra is an OSX-based text editor that uses Rendezvous protocols to facilitate real-time collaborative coding. It's from a dev team (Coding Monkeys) out of Germany. Real-time apps continue to excite and impress, and it's great to see different approaches — using Rendezvous, Flash Communication Server, Groove, or the new Microsoft P2P SDK.