Racer is great at synchronizing objects, and more flexible than Derby. One key difference between Racer and Telepat is that the Racer client needs to run within a JS container, while Telepat offloads native functionality to native clients. I'd say we're more mobile and user-access oriented than Racer, basically, but we're more architecturally apart as well.
EDIT: looks like the comparison is Derby only - racer is a bit more flexible IMO