A little history: GNU


The GNU project was born in  1984 when Richard Stallman,
then MIT employee, needed to go on sharing CS
culture with his own mates, without being bound
by restrictive licenses and unneeded secrets.

The main features of the system are:

Feature 0: it can be used for whatever purpose
Feature 1: it can be studied and customized
Feature 2: it can be copied with no royalties
Feature 3: it can be modified and redistributed