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|Original author(s)||Chris Schoeneman|
|Developer(s)||Chris Schoeneman, Nick Bolton, et al.|
|Initial release||13 May 2001|
1.8.8 / 23 March 2017
|License||GNU General Public License, version 2|
Synergy is a software application for sharing a keyboard and mouse between multiple computers. It is used in situations where several PCs are used together, with a monitor connected to each, but are to be controlled by one user. The user needs only one keyboard and mouse on the desk — similar to a KVM switch without the video.
Released under the terms of the GNU General Public License, Synergy is free software. Downloads are no longer offered for free and require a one-time payment of $19 for the Basic edition or $29 for the Pro edition.
The first version of Synergy (created on May 13, 2001 by Chris Schoeneman, also known as "crs") worked with the X Window System only, but later versions of Synergy support Windows, macOS, Linux, and other Unix-like operating systems.
A fork of Synergy named Synergy+ was started in 2009, but this fork project has since been merged back into Synergy.
Once the program is installed, users can move the mouse "off" the side of their desktop on one computer, and the mouse-pointer will appear on the desktop of another computer. Key presses will be delivered to whichever computer the mouse-pointer is located in. This makes it possible to control several machines as easily as if they were a single multi-monitor computer. The clipboard and even screensavers can be synchronized.
Architecturally, the program is implemented as a server which defines which screen-edges lead to which machines, and one or more clients, which connect to the server to offer the use of their desktops. The keyboard and mouse are connected to the server machine.
Prior to version 1.4.11
Communications are not encrypted, with key presses, mouse movements and clipboard contents sent to Synergy clients easily able to be sniffed on network traffic.
It is recommended that if Synergy is not being used on a trusted local network, that all communications be tunneled through a secure encrypted connection, such as through SSH, stunnel, or a VPN. In this model, the Synergy server computer needs to be running an SSH server, and the Synergy process should be configured to listen only on localhost.
Version 1.4.11 to 1.6.3
Between version 1.4.11 and 1.6.3, communications could be encrypted and key presses, mouse movements and clipboard contents could be encrypted prior to being sent to Synergy clients.
In July 2013 the Defuse Security Group reported the encryption used in the Synergy protocol be insecure. They released an exploit, which could be used to passively decrypt the commands sent to the Synergy clients. This was solved with the introduction of SSL in version 1.7.
Version 1.7 onwards
As of version 1.7, encrypting of communications between clients requires the purchase of the Pro version, with the previous encryption being replaced by SSL. It is still possible to enable encryption by manually compiling the code.
Synergy+ was created in 2009 as a maintenance fork for the purpose of fixing bugs inherited from the original version. The original version of Synergy had not been updated for a notable length of time (as of 6 June 2010, the latest release was 2 April 2006). There was never official confirmation that the original Synergy project had been abandoned; however, there was public discussion providing speculation. In said discussion, Chris Schoeneman (the creator of Synergy) stated that instead of supporting a 1.3.x team, he intends on releasing version 2.0 of Synergy, and publicly announced on 27 Aug 2008 that he has been making progress on this version.
The first incarnation of Synergy was CosmoSynergy, created by Richard Lee and Adam Feder then at Cosmo Software, Inc., a subsidiary of SGI (née Silicon Graphics, Inc.), at the end of 1996. They wrote it, and Chris Schoeneman contributed, to solve a problem: most of the engineers in Cosmo Software had both an Irix and a Windows box on their desks and switchboxes were expensive and annoying. CosmoSynergy was a great success but Cosmo Software declined to productize it and the company was later closed. Synergy is a from-scratch reimplementation of CosmoSynergy. It provides most of the features of the original and adds a few improvements.
On 20 June 2010, a Synergy+ project leader requested that the Synergy+ project take over the original project  under the SourceForge.net Abandoned Project Takeover (APT) system. The maintainer of the Synergy project (Chris Schoeneman) denied this request two days later.
The two projects merged two months later, at which point a new website was created under the original Synergy project name.
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 developers claim only
0.002% of people were donating to fund the development before charging.[better source needed]
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