Should I use a permissive license? Copyleft? Or something in the middle?

The open source license you choose for your project, or for the projects you choose to contribute to, can have significant effects on how what you contribute is used. One question that has garnered quite a bit of interest recently is the fall in popularity of copyleft licenses in favor of permissive licenses. An article last year looked at the issue of large number of projects on GitHub that have no explicit license and posited the question about whether we live in a 'post open source software' world, where seemingly open source software has no license. After some time, GitHub agreed that licensing is important and worked to improve the situation with a license chooser.