Not all GTFS-realtime feed producers provide an easy way to get a human-readable version of the feed, and I have seen that this can be a barrier for new developers trying to understand an unknown feed. Of course, most Protocol Buffers libraries provide an option for text output, but if you just want to quickly see the contents of an unknown feed, it can be a minor nuisance.
So, I've put together a quick Java command-line tool to dump out a GTFS-realtime feed from a file or URL:
The tool doesn't do anything at all novel, but it marginally reduces the barrier to entry by providing a portable, packaged-up, no-dependencies way to examine an arbitrary GTFS-realtime feed.
-Kurt