Hello, I work on Pharo, an open source derivative of Smalltalk. Pharo is licensed under MIT hence most of my work needs to be licensed also under MIT.
However, time to time I have some projects in my free time that I made for my personal usage or for friends, and in those cases I am not OK with my work being used by for-profit project not giving anything back. I would very much prefer to use GPLv3 on those cases, but my understanding of licensing is very poor and I have been told there is a “virus” behavior on GPLv3 that may prevent people to use at all what I do, and that’s not my intention.
Do you have any advice how to handle this?
Sort of. And this “viral” nature applies to all copylefted licences (GPL1, GPL2, GPL3, AGPL, CC-SA).
You can take GPL3 code, use it, and then close off your own source, as long as it’s for private purposes. What you can’t do is then distribute it under different terms. The GPL says that if you take GPL code, modify it (make a “derivative work”), and then redistribute it, you must redistribute it under the same terms that you got the original code from. So your users must have the same rights that you had when you got the original code.
Thanks for the additional clarification!