For me it was the philosophy behind Free (as in freedom) software. Call me a Richard Stallman fan, but I would love to live in a world were everyone is free to:

• Run the program as you wish, for any purpose.
• Study how the program works, and change it so it does your computing as you wish. Access to the source code is a precondition for this.
• Redistribute copies so you can help your neighbor.
• Distribute copies of your modified versions to others.

Learn more at fsf.org