There's a few cloud storage sync'ing tools hidden away in the Dev subforum, if you're into that sort of thing.
If you happen to have Calibre on hand, there's also @sherman's
UNCaGED app, which acts as a Calibre Wireless client (much like the Android app you may be aware of).
(We should have caught the brunt of the issues by now, so you don't necessarily have to be scared away by the "alpha" label

).
Other than that, KOReader has an OPDS browser, but that might be a tad overkill if your only use of it is for that, especially because getting Nickel to pickup new data when it's not being used at all is a bit tricky

.