Probably not Google, they do have a process for open source contributions though it is pretty expansive - technically you need approval for answering a Stack Overflow question with a code snippet.

They do approve side projects in rarer cases where it has nothing to do with Google's business - for example, my friend recently wrote an app for sex positions. But most things that I want to work on have a messaging / ML / AR component to them somewhere so I haven't felt comfortable building anything while I've been employed there. Hence the main reason I'm leaving Google at the end of the month, to build those things :)