I think that parts of Google Wave’s OT implementation are Open Source (and more parts are coming).
I’m not sure if this is what you are looking for, but an alternative to OT is Differential Synchronization:
- Google-Diff-Match-Patch – Diff, Match and Patch libraries for Plain Text: “The Diff Match and Patch libraries offer robust algorithms to perform the operations required for synchronizing plain text.“
- Google-MobWrite – Real-time Synchronization and Collaboration Service: “MobWrite converts forms and web applications into collaborative environments. Create a simple single-user system, add one line of JavaScript, and instantly get a collaborative system.” (Uses Google-Diff-Match-Patch.)