Ubuntu is a free Linux distribution based on the powerful and stable Debian platform. Ubuntu is an African word meaning 'Humanity to others', bringing the spirit of free software. Current version is 8.04 which means its release date (April, 2008), and every six months a new version is released.

Ubuntu is supported by a huge community of users and developers worldwide, help is most through forums.
Ubuntu comes with a series of already installed applications that are categorized by functions like:

Accessories: many useful applications
Games: blackjack, solitaire, and many others
Graphics: Gimp
Internet: Mozilla Firefox, Email Client, Messenger
Office: Spreadsheet, Word Processor, Presentations
Sound & Video: Multimedia Players.

You can run Ubuntu as a desktop operating system or with the same distribution configure it as a powerful and secure Web Server, FTP Server or File server among many other uses that a Linux Server will bring you. Ubuntu can be run without destroying your current OS installation, just boot from their Live CD and it will boot and completely function as it was installed on your hard drive, even you can access your current files and folders stored on your hard drive.

Also you can install this version of Ubuntu as a windows application that will no interfere with your windows installation.