Usenetic was released 2 years ago.
Usenapp is more or less the next version of Usenetic with many more functions.
Usenapp has been completely rebuilt and more importantly, it has a built-in "Newsreader", which Usenetic does not have.
Usenetic is more focused on binaries, while Usenapp supports both binaries and text messages.
You can also search NZB files on your favourite NZB indexer with Usenapp.
You can try Usenetic for free and see the differences for yourself.