I have an app that I want to make open source, as in the literal definition of the code being public. Github says that if you don't apply a license, it's copyrighted by default. I want that, to be the only one who can distribute the app, sell it, etc. Customers can download the code and build it if they're tech savvy enough but otherwise I'd like to charge a buck for an easy .zip/.dmg download link on a website. But I'm also open to contributions if in the future someone wants to.
However, according to https://opensource.guide/legal, "If you don’t apply an open source license, everybody who contributes to your project also becomes an exclusive copyright holder of their work. That means nobody can use, copy, distribute, or modify their contributions – and that 'nobody' includes you." That last part stumps me. They can contribute code but I can't use their contributions so it's like why did they even contribute. I want contributors to retain credit for their work, but I don't want someone to be able to distribute and sell my work just because they added one line of code to it.
Do you see what I'm saying? I'm not trying to get put out of business here by my own app's doppleganger somewhere out there on the web. By all means, make my app better and put it on your resume, but forfeit your selling rights to me!