The Omni Group has released OmniPresence, bringing automatic document syncing to OmniGraffle, OmniOutliner, and OmniGraphSketcher. OmniPresence is designed to work with any Mac app that supports OS X’s Auto Save and Versions. It also lets your Mac, iPad, and iPhone apps know when a document has been edited on another device and syncs the latest copy of any document to them. It supports document syncing for teams as well, ensuring the entire group always has the latest document available on all their devices.
Another nice featured noted in The Omni Group blog is that, while it can't prevent conflicting edits, if a document is being edited at the same time from two different devices, it detects multiple edits and saves both versions so that no edits are lost. Check out the video for more.