Observable - Interactive code examples/posts
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.
nbviewer.org - Rackspace server host Jupyter Notebooks from your github repo
Boostnote - Boostnote is an open-source note-taking app.
iPython - iPython provides a rich toolkit to help you make the most out of using Python interactively.
Binder - Turn a Git repo into a collection of interactive notebooks