Collaborating on Jupyter Notebooks
CoCalc provides Jupyter notebooks with realtime collaboration, unlike Colab, Kaggle, etc.  You just make a project drag and drop ipynb and data files, add collaborators, and everybody can edit everything simultaneously.  You can also share content publicly at the share server.   I think CoCalc is currently the overall most mature of the realtime Jupyter collaboration platforms (and it is the only open source one 4), but Deepnote is another option that is more focused on data science (but is closed source).