Allway Sync synchronizes multiple copies of files on all your devices: PCs, laptops, removable drives, and more. Its algorithms detect the most recent changes, no matter which device you make them on, and update everything with true bidirectional synchronization. Data is logged in a local database for privacy and security. Allway Sync is free for personal use with limitations.
Advanced synchronizer: During setup, you can opt to install a Windows service that synchronizes data automatically at the system level without requiring you to log in.
Multiple platforms: As its name suggests, Allway Sync updates data on many different devices, like PCs, laptops, remote servers, USB drives, and other online storage solutions; encrypted data, too. Mobile apps are available, too.
Jobs: You can create and even clone Jobs for frequent or large sync batches.
Easy-to-use interface: While Allway Sync's user interface isn't exactly attractive, it's easy to figure out.
Freemium: Allway Sync is free for "moderate personal use," which means up to 40,000 files in 30 days. Heavy users and businesses are advised to upgrade to Allway Sync Pro.
Time conflicts: According to the documentation, Allway Sync can have issues synching files when one or more PCs in the loop has a system clock error, which is all too common in Windows PCs.
Allway Sync has some nice features, and most private users won't notice the free version's limitations. It's well worth trying Allway Sync head-to-head against other free-with-limits sync services, like Dropbox.