Node.js . I whined about how it's silly to have a backend written using a front-end language, but I also run a forum which is written in node.js. Why? Because I didn't have time and I got sick of PHP lol.
Same thing. First time I heard about Nodejs (around 2009 or 2010), the idea of running javascript on a server sounded like an heresy to me.
Then I gave it a try, and when Typescript came out (was a very earlier adopter to write some front-end js sdk) I started to use it for real. But when it was released I never thought I would write and run js on a server!