This page lists good quality free and open-source software that anyone can download at no cost and use or modify freely. Plenty more quality open-source software exists – this is just an introductory sample. Most of these programs are cross-platform, meaning they can be installed on MS Windows, Mac OS X and Linux.
The software below is not freeware or shareware, which are both significantly different to open source.
Ubuntu - Linux distribution with full compliment of software for everyday use. See also Kubuntu that runs the KDE desktop which some people find this easier if they previously used MS Windows. Ubuntu is an easy to use operating system based on and made possible by the Debian project.