The tiny program hiding in your car, TV, and phone

You may have never typed it, but you almost certainly use curl every day. Short for "Client for URLs," it's a small open-source tool for transferring data to and from servers. Created by Swedish developer Daniel Stenberg in the late 1990s and still led by him today, it's written in C and split into two parts: the curl command-line program, and libcurl, a reusable library that other software embeds to do networking.

That library is why curl is everywhere. It ships inside cars, smart TVs, routers, printers, game consoles, phones, and countless apps and operating systems — by the project's own estimate, it runs on well over ten billion installations, making it one of the most widely deployed pieces of software on Earth. Most people benefit from it without ever seeing its name.

Part of curl's power is breadth: it speaks dozens of protocols — HTTP and HTTPS, of course, but also FTP, SMTP, IMAP, POP3, SCP, and more — behind one consistent interface. For developers it's the go-to way to test an API, download a file, or script a web request in a single line, like curl https://example.com.

A surprising twist: because curl is embedded in so many devices, Stenberg has been contacted by frustrated car owners asking him to fix their vehicle — mistaking the name in the license screen for a support line.