Note: Replace all USER with your primary user name.

These instructions have been tested on Debian and Ubuntu.

1. Install unison (and unison-gtk) and curlftpfs:

   aptitude install curlftpfs unison unison-gtk

2. Setup a local mount path:

   mkdir /mnt/shared

3. To be able to mount the shared directory as a normal user, add your user to the fuse group: adduser USER fuse
4. Next, the directory must be user/group writable: chown USER:fuse /mnt/shared
5. Modify /etc/fstab to contain the fuse entry:

   curlftpfs#user:password@host /mnt/shared fuse rw,uid=1000,user,noauto,allow_other 0 0

   Replace uid=1000 with the number of your primary user. Issue the command id -u to get the uid value.

6. Sometimes it is also necessary to allow fuse to be mounted by other users, edit /etc/fuse.conf to have the option user_allow_other. Add the entry if missing or uncomment it by removing the # character.
7. Create a synchronization directory in your home: mkdir ~/syn
8. At this point it is necessary to log in and out again. This will re-read the group information. Or create a fresh login using su - USER and entering your password.
9. Mount the directory (it is not mounted automatically): mount /mnt/shared
10. Start unison: unison-gtk and specify ~/syn as local and /mnt/shared as remote site.

A good tool is provided by Microsoft, it's called SyncToy.