SyncEXP

SyncEXP is freeware for file and folder synchronization software for Windows.
SyncEXP uses innovative synchronization algorithms to synchronize your data between desktop PCs, laptops, USB drives and more. SyncEXP combines bulletproof reliability with an extremely easy-to-use interface. Thanks to its smart data comparison approach, the sychronizing speed is second to none. You will save minutes to hours of computation resources over our competitors if you are processing over tens of thousands files.
The synchronizer is free to use in full features for all and any purpose, including personal, academic, and commercial usage.
SyncEXP is a green software (or a "widget" as some will call) which is free from dll and can be run from USB disk. No installation to the client computer is ever required. It works even if software installs are prohibited. When USB disk is pulled out, the synchronizer detaches from the computer.