What a great idea: an app that synchronizes disparate iTunes libraries on multiple computers in a network. It sounds awesome. Imagine, having all your computers with identical iTunes libraries containing the best of all possible worlds. Unfortunately, TuneRanger ($30, buy-only) doesn't perform adequately, and is thus kept out of contention.
The main beef with TuneRanger is that it doesn't respect music folders. I scoured the Help files and the options for the ability to keep music folders when merging, but to no avail. When merging multiple iTunes libraries, TuneRanger throws up all your music files into the iTunes Music folder in one big lump, regardless of what folders those files were located in on the other networked computers. What TuneRanger really needs to do is create folders locally and remotely and keep those music files organized when syncing. Having thousands of music files in a single folder is useless and impossible to manage.
Then there are the functionality issues. After halting a massive sync in progress, the app seemed stuck on the last song it tried to sync. I couldn't clear this information from the user interface, even after quitting and relaunching the app. Only halting the resident portion of TuneRanger in Task Manager fixed it. I also found a repeatable crash bug: when using the Save Album Art to Music Files feature and executing on files it found without album art, the app crashed. I was able to repeat this bug twice on a desktop PC and a laptop, both running Vista and iTunes 184.108.40.206.
TuneRanger is the only app I could find dedicated to syncing iTunes libraries; in order to keep your libraries straight, you might be better off using a document syncer like Google Sync and simply rescanning your library with iTunes (so it knows about the new music) every so often.