Similarly, I've been writing respectable, sophisticated software for decades but I'm fairly certain that my most widely used piece of software, by a wide margin

Similarly, I've been writing respectable, sophisticated software for decades but I'm fairly certain that my most widely used piece of software, by a wide margin, is a mildly pornographic app (http://driftwheeler.com http://driftwheeler.com) Other projects I've published have a trickle of users. But this app, published in 2017, has a continuously growing population of users from all over the world. I get email every day asking whether soft1 is the only server, thanking me, suggesting improvements, etc. It's ironic, and there is a difficult lesson to be learned from this reality.