When looking at ways to upgrade a Windows or a UNIX-based server, one of the major decisions you'll make is whether to use a "manual" method in which you install Unison on your computer or use an automated tool, such as the OpenSSH server. Manual methods require you to download and install Unison on every machine you want to join the network, configure its settings, and then configure your connection to the file system. Once you've downloaded and installed Unison on your computers, you will then be able to log into your servers as a user, creating a fully-functional remote server (even if you don't have a thumb drive handy). In contrast, using an OpenSSH server allows you to connect to your existing UNIX machine without downloading anything and has significantly less potential downtime.
One of the key benefits of using Unison is that it supports both SSH and HTTP protocols. Although the majority of companies who sell Unison products will indicate that only the latter is supported on their product (due to the licensing requirements for commercial usage), in practice anyone who has basic knowledge of either protocol can easily set up and run a UNIX-based server using Unison. As such, it's possible to connect your windows machines to a remotely located UNIX box using Unison.