Synergy works really well, it’s simple to use, and is an essential utility if you want to control local computers with a single mouse and keyboard.
The latest version of Synergy is 1.73; the application continues to be actively developed. Ubuntu Software Center offers an older version (1.62). But to upgrade to the latest version you now need to stump up $10 for the basic edition, $29 for the pro version (which includes SSL encryption), or compile the source code yourself. I’m not an advocate of open source software that charges money to download a binary with no other direct benefit. The developers of Synergy say this route is essential, as only 1 in 500 users were donating to the project. But as most individuals will not try to compile the source code, and with no free trial available, the latest version is essentially off limits without people having to pay. This isn’t a good model for the sustainable development of the project.