Linux is an OpenSource Operating system for servers, desktops and laptops. Linux is "mostly" free. There are many flavors of linux called "distributions." Here are few popular distributions:

Ubuntu

SuSE

Madriva

Fedora Core

http://www.ubuntu.com/getubuntu/download

http://software.opensuse.org/

http://www.mandriva.com/en/download/free

http://fedoraproject.org/en/get-fedora

Open Office is a free office software product. It is similar to Microsoft Office and Corel.

Openoffice