Kaggle

Kaggle is Google's data science community where you can run Python and R notebooks in the cloud with free GPU and TPU time. It pairs those notebooks with a large library of public datasets and models, plus machine learning competitions with prize money.

Notebooks open in the browser with common ML libraries preinstalled, and any public dataset or model can be attached in a few clicks. You can fork other people's notebooks, publish your own, and keep them private or share them with collaborators.

Beyond notebooks, Kaggle hosts competitions run by companies and research groups, short free courses, discussion forums and progression rankings. Accelerator time is free but comes with a weekly quota and session time limits.