Debugger and Compiler. Support for many languages and versions including(but not limited to) #python, #javascript, Pascal, #HTML, #CSS, C, C++, Perl, Ruby, C#, and PHP.
Allows you to make multiple file programs. onlinegdb.com
3)Codepen
Don't want to code alone? Codepen has a big community where you can find inspiration as well as learn via challenges.
Want a simple interface and cool-looking place to code your problems away? It also has a dark mode. Although it only has a few (most common ones) languages supported yet, and still seems to be in beta
Offers a #VScode like experience, so you don't feel too different.
It's also full of surprising features you don't even find on many desktop applications. (not all of those features are free) stackblitz.com
And that's all.
In the end, it doesn't matter where you code.
What matters is that you code.