Free operating system for your desktop or laptop
Faster, smoother, more beautiful…
New features, fixes and applications designed around you
Developing at speed…
Fun tools make it write and deploy apps to Ubuntu
…and introducing your personal cloud
Store and share files and contacts in a couple clicks with Ubuntu One

What is Ubuntu?

Ubuntu is an operating system built by a worldwide team of expert developers. It contains all the applications you need: a web browser, office suite, media apps, instant messaging and much more.Ubuntu is an open-source alternative to Windows and Office.Discover Ubuntu »

via Ubuntu Home Page | Ubuntu.