Can this be used to sync the data of an app from mobile to desktop without a server ? And vice-versa.

In principle but we don't yet support mobile except experimentally, in part due to mobile OS restrictions (eg. iOS apps can't embed webassembly).

But not a problem in theory for Android and Ubuntu Touch systems?

	▲	sanity 2 hours ago \| parent [-]
		Yes, iOS is the main headache. The other issue is that people probably won't want it using their mobile network bandwidth in the background, but that's solvable.