It was twenty years ago today that I quit my job at MIT to begin developing a free software operating system, GNU. While we have never released a complete GNU system suitable for production use, a variant of the GNU system is now used by tens of millions of people who mostly are not aware it is such. Free software does not mean „gratis“; it means that users are free to run the program, study the source code, change it, and redistribute it either with or without changes, either gratis or for a fee.