Factorio is a wonder of software engineering. The authors amaze me at the level of performance they keep getting out of the game, but still find new improvements.
There is something amazing about watching 500 players in the same world all building a giant factory together. A great visualization of collaborative software development if ever I saw one.
The blog https://www.factorio.com/blog/ which the devs kept running since nearly the inception of the game when they had no idea if it was going to succeed, to now when it has made them rich, is a great lesson in perseverance while also having some great technical tidbits.