This is a web app that returns your useragent to you in plain text. The tricky bit: it's written in Brainfuck.
# clone this and cd inside
npm install
npm start
Visit it at http://localhost:3000. Try hitting other URLs to notice your 404 errors!
I wrote a small Node server (server.js) that's kind of like CGI for Brainfuck. It takes the bytes from a TCP stream and sends them to Brainfuck (server.bf), responding with the Brainfuck program's result.