I read "work for free" as doing open source work, at least by contributing to projects you make use of regularly, which I whole-heartedly recommend. This alone

I read "work for free" as doing open source work, at least by contributing to projects you make use of regularly, which I whole-heartedly recommend. This alone has probably accounted for 50% of any success I've had in my career, in terms of making connections with other talented people, having publicly visible code (which has brought opportunities to me I was never even aware of), and of course honing my own skills.