Not only plain old copyleft relies on copyright, but also the model of publishing code under the GPL and charging for a commercial license. I have used three su

Not only plain old copyleft relies on copyright, but also the model of publishing code under the GPL and charging for a commercial license. I have used three such libraries in client work, and I absolutely love this model: - We can audit software before buying - We have the ultimate "right to repair" - Open source/hobby projects can automatically use it for free (SAAS/closed source projects often offer this as well, but there's more friction) And even if we are not technically required to upstream any patches that we make under the commercial license, the average engineering team will try to keep their downstream patches to a minimum, and the easiest way is to get them merged in the original GPL version.