Linux
Linux is a favorite and there's not much to explain here. It's distribution keeps it alive. I don't know code and I can have faith someone like me is auditing the code, to a degree- much more faith than a much more centralized approach where one person at one company signs off on approvals. Rather, by being Open Source, others are able to audit the code, and depending on the licensing either change it themselves or make general recommendations to change it based on forking.