Similarly, I've been writing respectable 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)

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 lesson to be learned here.