FreeFileSync

Does pretty much everything I need to do better than MS Synctoy. I had started off with that hearing good things until I found out it won't copy files that are in use. I'm using it to sync my XBMC database from my media center to my regular PC. It works like a charm. I also use it to keep my music synced across 2 computers (I like having it in both places) as well as my Portable Apps. It reads the changes ridiculously quick, copies files in use, and the interface stays relatively responsive.

If you're looking for the portable version, look in the v3.2 folder. That's where it paf package was.

Fastest way to install:
sudo apt-add-repository ppa:freefilesync/ffs
sudo apt-get install freefilesync

My personal impression: structured very clearly, and very impressing and simple user interface. But if You want to delete files on the other directory equal in what direction automatically, You cannot use it for synchronisation.
For this purpose there would be necessary a synchronisation data file in the synchronised directory, which FreeFileSync does not have and not need, because the deletion direction must specified from case to case. FreeFileSync is good for making identical copies of directories (Like backups in ONE direction)
Deletion automatically in both directions is possible with Synkron (Open Source), PureSync (Free for private use), totally perfekt with Allway Sync (but max. 20000 Files/month free, the only Sync Tool, able to sync Windows Mobile SD-Card or NAND-Memory and WebDAV and FTP-Online Memory direct adressable).