Google engineers who retire early might still work or contract part-time, or feel compelled to create completely new inventions with their newly freed minds.
This paragraph really jumped out and stuck in my mind, since I was in the busy midst of a software engineering career when I read it. Here I am several months after retiring (from traditional employment only!) and it has panned out! I have built a free assistive tool aimed specifically at repetitive-strain-injury, which is not well served by typical assistive technology aimed at more serious disabilities.
https://farfetchd.github.io/clickitongue. Try it out and/or share it, if you and/or someone you know has RSI problems!
With this project done I'll be moving on to something new (other than continuing to support it, of course). This time it'll be for profit, but the fact that I could just continue right on with "make the world better with no hope of making money" work if I so chose is amazing. Only slightly less amazing is being able to take a chance on something that only *might* make money, without even needing to visit MMM's Optimism Arsenal, while being as risk-averse/cowardly as myself.
I don't want this post to be publicity for my project (well not solely, lol), so: what new thing have you created and given to the world - for free or not - since getting to the second half of FIRE?