Ubuntu is a complete Linux operating system, built and supported both by professionals and the community. It's completely free, and will run on just about any computer desktop or laptop. Canonical, the folks behind the Ubuntu project, are also working on bring the same experience to mobile devices like phones and tablets.
Ubuntu is trying to unify the mobile and the desktop experience
Ubuntu and Android have a long history. In fact, the folks at Google who write and build Android are using Ubuntu to do it. With the most recent versions of Ubuntu, the same software (using the same installation package) runs on servers, desktop workstations, laptops, tablets and phones — including several Android models. Canonical is also working with partners like T-Mobile and EE to bring Ubuntu mobile devices to market. What was originally slated to be Ubuntu running on top of Android has now become a native mobile OS in its own right.
Sharing a common Linux heritage with Android, developers should feel at ease when designing both hardware and software for Ubuntu phones. Both BQ of Spain and the Chinese giant Meizu have signed on as hardware partners, and we should see the first Ubuntu-powered phones sometime in the near future.