Ubuntu is a community developed, linux-based operating system that is perfect for laptops, desktops and servers. It contains all the applications you need - a web browser, presentation, document and spreadsheet software, instant messaging and much more.
They have a server edition also.
The Server Edition - built on the solid foundation of Debian which is known for its robust server installations ? has a strong heritage for reliable performance and predictable evolution.
Integrated and secure platform
As your business grows, so does your network. More applications need to be deployed and more servers are required. Ubuntu Server Edition offers support for several common configurations, and simplifies common Linux server deployment processes. It provides a well-integrated platform enabling you to quickly and easily deploy a new server with any of the standard internet services: mail, web, DNS, file serving or database management.
A key lesson from its Debian heritage is that of security by default. The Ubuntu Server has no open ports after the installation and contains only the essential software needed to build a secure server.
http://www.ubuntu.com/