There are two versions: free and paid but the free has plenty features.

"PureSync by Jumping Bytes is a Windows program to synchronize files and folders, and to do backups e.g. automatically in the background.

Side by side compare view
Automatic synchronization and backups
NAS and FTP support
Easy to use but still many options
It's free*
* for personal use only"

Jumping Bytes Software - PureSync - Synchronize and backup files and folders