Synergy is free and open source, and always will be!.Make use of your Raspberry Pi on your desktop.Avoid needing VNC for computers close by (like a media center).Easily turn your old laptop or desktop PC into a second screen.Used by gamers for multiboxing (WoW and other MMORPGs).An alternative to a keyboard/mouse USB switch.Only a local network connection is needed (no extra cables or hardware).Seamlessly share your mouse and keyboard with two or more computers.Network-based (IP) software KVM switch, minus the video.Save space on your desktop by using one keyboard and mouse.

Encryption keeps sensitive data safe on public networks.

Drag and drop files from one computer to another.

Share your clipboard (copy and paste) between your computers.

Supported on Windows, Mac OS X, Linux, Android and Apple iOS.

Simply move your mouse to any computer and start typing.

Usage is as simple as moving the mouse off the edge of your screen. Synergy is supported on Windows, Mac OS X and Linux. No special hardware is required, just a network connection. Synergy is Free and Open Source Software that lets you easily share your mouse and keyboard between multiple computers, where each computer has its own display. Most open-source software comes with build files that enable you to enable/disable specific features where this is applicable.Do you have two computers at your desk, with two screens and two sets of keyboard and mouse? Here's where Synergy comes in. Yes, assuming you compile a build with all the features enabled. The developers claim only '0.002% of people were donating' to fund the development before charging. On 8 September 2014, the Synergy developers started charging a fee for distribution of pre-compiled binary files of Synergy on their website, while offering a free download for the source code. The paid versions you refer to in the question are for pre-compiled binaries as Synergy charges for distributing these on their website:

You don't strictly have to compile it yourself, someone else can build it for you, and the developers cannot restrict people sharing built binaries as long as it is GPL licensed.

Released under the terms of the GNU General Public License, Synergy is free software. Yes, it is free as it is under the GNU General Public License. Is Synergy free if you compile it yourself?

Synergy 1.8.8 sourceforge