Acrosync for Windows can sync entire folders with any Linux/Mac/NAS without installing server software. That is because it is the only native Windows implementation of rsync, a powerful folder sync tool that is ubiquitously installed by default in the non-Windows world.
Acrosync for Windows is not dependent on cygwin and it is very easy to install. Just download a small installer and a few clicks later you're ready to go. An ssh client is built-in, so there is no need to setup password-less login for rsync over ssh.
Moreover, not depending on cygwin also means that, had there been any issue, we can fix it and send you a new executable within 24 hours in most cases.
Acrosync integrates a file system monitor that can detect file changes. Using the automatic upload mode, new or modified files will be automatically and almost instantly uploaded to the rsync server. File deletions can also be automatically propagated to the server if the 'propagate deletions' option is selected.
If you currently rely on Dropbox to automatically sync file changes from one computer to another, you should switch to Acrosync, which has no limits on storage and costs a low one-time license fee (after 15 day free fully functional trial).
When run as administrator, Acrosync can invoke the Volume Shadow Copy service prior to opening files. This way, files locked by other processes can still be uploaded, guaranteeing consistent backups on the server.
When this option is selected, Acrosync is capable of creating space-efficient incremental hourly backups on the server, taking advantage of the '--link-dest' option provided by rsync. This essentially turns any Mac/Linux/NAS into a Time Machine style backup server, without installing server software and at no extra cost.
Acrosync can connect to almost any Linux computer even without server-side configuration. This includes not just desktops but also servers, such as VPS or dedicated servers. A remote access acount provided by most companies and universities works too. Or even a small form factor computer like Raspberry Pi.
For Mac, the 'Remote Login' option in System Preferences should be enabled. For windows, cygwin is recommended and then openssh and rsync packages must be installed.
Acrosync syncs with most NAS boxes out of the box. QNAP and Synology ones are officially supported.
HiDrive and Strongspace, which are rsync storage providers, are officially supported as well.