Best File/Folder sync software (on-the-fly)?

FreeFileSync now has a real-time option. I personally don't use that feature because I don't need it but it may be worth a try.
http://freefilesync.sourceforge.net/

You are welcome Mike and by the way welcome to seven forums.

if you have a hotmail account then you could download and install live mesh this will sync between computers and if you want you can have a folder or more to upload to the skydrive, you can store 5GB in it and its free.
just drop a file in your folder and it backs up to your account automatically.
real handy

to get it you have to install live essentials ,but on the install window uncheck the extras you dont want like messenger and photo gallery, though i recommend photogallery also.

Also FreeCommander has a Folder Sync function with a UI similar to Free File Sync. It's strictly manual though. However you can set up Layouts to save the configuration of tabs under a name. Select a Tab on each side and hit the Sync Button. It optionally includes subfolders and is easy to use. Pretty much fool proof. After you hit Compare it shows which files will be copied in which direction. You can remove items from the list. Then after you hit Sync it shows a summary. If you only want to sync in one direction just uncheck the target on a side etc..

Tutorial link
FreeCommander - freeware file manager

Download link
FreeCommander - freeware file manager

Hi tolinho and welcome to Seven Forums.

The real time option is a separate program called realtimesync which gets installed when you install FreeFileSync. I've not used it myself but I understand that you create a batch file in FreeFileSync and you then add it to RealTimeSync. The instructions are in the help file for FreeFileSync.