Ondřej Mirtes, author of PHPStan lists some great tips to make a side project succesful.

Most developers have side projects. That's how we try out new things or make something that we miss on the market or in our dev stack. But most side projects end up unfinished and never actually see the light of day. And even if a developer builds up the courage to show his work to the public, he quickly finds out that just publishing a repository doesn't actually bring the masses to his doorstep. ... In this article, I'd like to share with you what I did to make sure that the project doesn't end up in the dustbin of history. I will concentrate on open source software, but the following advice may as well apply to any creative endeavour.