[nonsince]

It's different for me, since my company uses a relatively obscure language (Rust, it might not seem obscure if you hang around on HN but most people just look at you quizzically if you bring it up), but contributing to the compiler and having a library that was being used by a reasonably well-known project was very helpful. I think the single biggest factor in me getting hired was a couple of blog posts I made, however. Nothing proves your aptitude for software to a company than having an extended, long-form writeup of your thought process. Even if you're not that great a writer it's extremely useful to have a technically-focussed blog that a prospective employer can read through.