I think it depends a lot on how valuable your software can be to $supermegacorp, honestly. If I write a competitor to $bigproprietaryapp I would probably decide

I think it depends a lot on how valuable your software can be to $supermegacorp, honestly. If I write a competitor to $bigproprietaryapp I would probably decide to release it under a more copy-left license just so nobody can take a ready-to-run solution to market without recourse or compensation. I don't have a problem with proprietary software extending things I write, so such an app would probably be under something like the MPL - "you can use this and add extra features without contributing them back, but you still have to give changes to my code back" sounds like a pretty good compromise. Some big company wants to use the silly little structured logging wrapper I wrote for SLF4J though? What do I care, go for it, it's a tool and your use of it has no ability to damage any use the community at large has for it.