Tool that hooks to two directories and synchronizes them as soon as something changes

I have huge simulation directories on the two machines server and on cluster which I want to keep synchronized. The basic situation is that files rarely change but when a simulation is done many big files change at once which I'd like to have synchronized as soon as they are closed.

Therefore I assume a cronjob using rsync is not ideal, cronjob because it calls rsync at a fixed time interval which I'd probably choose either too large or to small, rsync because it shouldn't have to check for modifications of files since I and the simulation job are the only ones accessing them.

So my idea would be using inotify (see this question) to detect changes in the simulation directory in a loop and then fork into a rsync for the changed files. However I'm not sure whether that might accidentally skip files closed just when the fork is done. _{(and possibly I'd also end up in an infinite loop due to inotify calling rsync to sync the just synchronized file again…)} So before I try too much there, I repeat my question:

Is there a tool that hooks to two directories and synchronizes them as soon as something changes?

(basically this would be something like an offline dropbox, I guess)