the.com/copyleft
copyright's rebellious sibling: you can steal this, just share your loot the same way.
means a licensing trick that uses copyright law to guarantee software (or its derivatives) stays free and open forever, instead of getting locked up.
from coined in the 1980s by Richard Stallman and the GNU project, riffing on 'copyright' with a pun scrawled on a letter that said 'copyleft — all rights reversed.'
first licenseGNU GPL launched the whole idea in 1989
the trickuses copyright to enforce openness, not restriction
viral clausederivatives must stay copyleft too, forever