Ask HN: What open source projects have had mass consumer adoption?

I constantly see developers on HN talking about open-source consumer projects they've worked on, or open-source alternatives of popular start-ups. I appreciate open-source as much as the next developer, and I often use Apache projects, GNU's Not Unix tools, or open-source repositories in my projects. I struggle to think, however, of consumer-oriented open-source projects that have been successful. I know that open-source tools are the foundation for many start-ups, but I'm wondering about software that was actually developed for consumer end-users. The only ones I can think of are Firefox (but Mozilla is really run like a corporation that just so happens to be nonprofit) and 2048.