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?