Open Source has been around for quite some time, but odds are most people you ask won't know what "open source" is. This isn't because open source is obscure, but rather it has slipped into the mainstream, and unless you're already in the know, there's no real reason you will have noticed it.
So I bought two seats of Parallels a week or so ago. I couldn't resist: It was buy one, get one free. (And still is through December 31st.) Now my desktop Mac at work and my MacBook Pro drive the latest versions of OS X Leopard, Windows Vista and Ubuntu Linux, all from the same desktop, running in ... parallel. Who needs to choose between Mac and PC when there's Parallels?