Syncthing, GoodSync, Resilio Sync , Jungle Disk, DirSync Pro, SyncTrayzor, Autosync, CmisSync, Maestral, luckyBackup, Cryptsync, Dropsync (Dropbox Autosync), SyncMate, AutoFileMove, Cucku Backup, AllSync by Michael Thummerer Software Design, Syncness Wifi Sync Music/Files, Auslogics BitReplica, Virtual Drive Backup are some alternatives to FolderSync.