Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Observable - Interactive code examples/posts
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
nbviewer.org - Rackspace server host Jupyter Notebooks from your github repo
Slack - A messaging app for teams who see through the Earth!
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.