The volumes, Free as in Freedom 2.0 and Free Software, Free Society: Selected Essays of Richard M. Stallman, 2nd Edition are both now available from the FSF store as free downloadable PDFs and as signed copies. Signed hard copies cost $50 each.
And while you're shopping, you can also pick up a stuffed baby gnu, the FSF mascot, for $25.
The free-software activist launched the GNU Project in 1983 to create a free Unix-like operating system. He also founded the Free Software Foundation in 1985. The Linux kernel was built on and still supports GNU Project components that came before it and laid the foundation for open-source operating systems.
Stallman is also the main author of several copyleft licenses, including the GNU General Public License, the most widely used free software license.
Stallman's life work revolves around freedom, by which he means four things:
The software should be freely accessible.
The software should be free to modify.
The software should be free to share with others.
The software should be free to change and redistribute copies of the changed software.
These principles underlie and inform the free and open-source software movement, and they also are used in many of the arguments for Creative Commons licensing for art and music.