Jake is an interesting twist on file syncing and sharing apps, in that it uses XMPP as transport and embodies a concept that I and a few of my colleagues had been discussing a couple of years ago but never got round to implement (probably because I tried to get rsync into the mix, which would be nice but too complex). Unlike Dropbox it has no requirements for a central server - only for an XMPP server to act as meeting point and reflector.
Sadly, it is written in Java which makes it cross-platform but finicky.
p=.