The Creative Commons License - CC BY-SA 4.0 International

Stack Overflow was trying to go through and change everything to MIT. But their community was like, no, I want the attribution and all that kind of stuff. And so it never happened. So unless you're potentially willing, here's the thing. This is one of those ones that's not very clear on what build upon the material means. That can mean, hey, your code is using that code, so you're building upon it. If that's a case, you have to open source your entire application.