tsync:

provides transparent synchronization across a set of machines for existing files and directories. A transparent synchronization system makes keeping a set of files consistent across many machines---possibly with differing degrees of connectivity and availability---as simple as possible while requiring minimal effort from the user and maintaining security, robustness to failure, and fast performance....

In the Tsync usage model, the user writes a simple configuration file, similar to /etc/exports, describing which directories should be synchronized, and listing one or more other hosts that are part of the Tsync group (although this list does not have to contain all the hosts in the group). The user runs the Tsync daemon, tsyncd, on each machine in the group. Then when the user creates/modifies/deletes files on one machine, those changes are automatically propagated to all the others. So if the user were to add a bookmark on her machine at the university, it would be reflected on her desktops at home. Even if not all of the computers are connected at the same time (such as if her laptop were powered off), then the next time the disconnected machine regained connectivity, it would automatically learn about the change and update itself.