Martin
Understood about priorities. While adding rsync server capability might be just a simple two second configuration option in your build file, setting up the necessary runtime config files and testing would take much longer.
I'd be a happy to do the configuration and testing leg work for you but obviously I'd need to know what tool set you use and have the appropriate build files. No other support needed - and I obviously would not need source code for your b2 task either.
I'd also provide end user instructions on how to use it for incremental backups once incorporated.
Free offer - but I won't be offended if you don't take it. Send me details via email otherwise?
Tony