Ubuntu

Named after an African word for “humanity to others,” Ubuntu is a completely free distribution (based on Debian) fully developed by the Linux community. While this may be said for other Linux distributions, the real difference is in the ability (or right) that Ubuntu grants you to alter the software in any way that you want. To quote the developers, “Not only are the tools you need available free of charge, you have the right to modify your software until it works the way you want it to.”

Among the other public commitments the Ubuntu team makes, the team promises that the operating system will always be free, and there will be a new release every six months (each release is supported for 18 months).

More info and download here.