I have just released zsync v0.3.0. It is available on the download page. This version does not add any features, instead I have cleaned up the code a lot. The zsync process is now entirely contained in a library, and I expect to make this into a shared library which other programs could use in the near future.
The client program is quite simple now - it just contains the URL and HTTP code, and the housekeeping code for handling the downloaded files. It should be very easy to add alternative protocols now; I may have a go at writing a rsh/ssh file fetcher, to allow zsync to be used more like rsync (a popular feature request).
As there are some fairly deep code changes in this version, I would not be surprised if there were a few problems at first. Let me know if I have introduced any bugs.