GNU General Public License
nKey
terms:
nUnlimited
right to run program
nUnlimited
access to source code
nUnlimited
right to distribute verbatim copies
nMay
create derivatives IF you agree to make the derivatives “free”
nWhat
is a “derivative”
nWhen
does “free” mean “no charge”?
nLicense
is “viral”
nNo
warranties; disclaimer of consequential damages