The Free Software Foundation (FSF) didn’t begin with a manifesto or a press conference. It began with an ordinary piece of incorporation paperwork.
On October 4, 1985, five like-minded collaborators — Richard Stallman, Harold Abelson, Robert J. Chassell, Gerald Jay Sussman, and Leonard H. Tower, Jr. — incorporated a nonprofit, Free Software Foundation, Inc., in Massachusetts. In their application, they wrote that they hoped to encourage people to cooperate with each other by sharing software and other useful information.
By then Stallman had spent nearly two years on the GNU Project, a free Unix-compatible operating system he had announced in September 1983 and actually started writing in January 1984. He had already written the GNU Emacs text editor and was mailing it out on magnetic tape to anyone who asked — for $150 a copy.
For people without internet access, that tape was the only way to get the code. In effect, Stallman was running a one-man free software distribution business — the precursor of the companies that today sell entire GNU/Linux distributions.
As interest in Emacs grew, carrying that load alone became impossible, and the project needed steady funding. The foundation took over the tape business, then began selling other software on the same tapes along with printed manuals.
That revenue paid for staff in the following years: Roland McGrath wrote the GNU C library, and Brian Fox wrote the BASH shell.
A single programmer’s personal side project had become a legal entity that could accept donations, hire employees, and own the GNU Project’s infrastructure. Today the FSF remains its organizational home and the steward of the GNU family of licenses, including the GNU General Public License.
See also How the Open Source Movement Began on February 3, 1998.