Observable - Interactive code examples/posts
SmallDevTools - Handy developer tools with a delightful interface
nbviewer.org - Rackspace server host Jupyter Notebooks from your github repo
whatdevsneed - This is whatdevsneed.
Jupyter - Project Jupyter exists to develop open-source software, open-standards, and services for interactive computing across dozens of programming languages. Ready to get started? Try it in your browser Install the Notebook.
Utilso - All-in-one tools for developers