Repl.it is an online IDE wherein 2 seconds you can boot up an environment for your favorite programming stack or language. If you run a program that happens to open a port you've also just deployed an app that runs on our serverless platform. Before reading on, consider giving it a spin, no log-in required, you can play around with your favorite languages and libraries and maybe deploy a toy server just to see how it works (if we don't support your favorite language, tell us and we'll add it).
Start here: https://repl.it/languages (If you select one of the frameworks, hit run, a webview will open and that's it you've deployed).
We started working on what became Repl.it back in school where we were tired of setting up the development environment on every machine we wanted to code on. It was at a time where everything was moving to the cloud and we thought that, naturally, coding would follow suit. Because of that Repl.it's been popular among teachers, students, and more generally people learning to code because it eliminates the oh-so-painful setting up step. However, with the most-recent update -- where you can host websites, deploy web services and apps -- we're starting to see people use it for more serious side projects, small web-services, machine-learning projects, and in some cases production apps.
We've been so busy building and shipping that we forgot to update the landing page so it's a bit outdated. If you want to learn more about the direction that we're headed to please read my 1.0 announcement: https://repl.it/site/blog/platform