repl.it -- In-Browser IDE for Programming Code
repl.it is an IDE that works within your web browser. An IDE is an integrated development environment or application for helping to write computer programs or programming code.
repl.it works with 50+ programming languages, including Python, C, C#, Node.js, Basic, Machine Assembly and more.
It also lets you write HTML, CSS, and JavaScript webpage code, and run it, and host it.
It's very easy to collaborate and share with it.
And it's free. Code is public, but generally unlisted public, though if you just use your own name, someone may be able to find your code, though a lot of code get a "word salad" name, making it harder to search for it.
repl.it also has built-in classroom and assignment functions.
Collaboratory, classroom, and assignment functions require logging in.
You can use repl.it anonymously if you just want to quickly type in some code and test it.
Here is overview and demo video on repl.it