Now UI Kit - A beautiful Bootstrap 4 UI kit. Yours free.
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.
Bots UI Kit - Fully customizable Sketch UI Kit for Messenger Platform
Kajero - Interactive JavaScript notebooks - create good-looking, responsive, interactive documents.
Landing UI Kit - Handcrafted UI components for landing pages
BeakerX - Open Source Polyglot Data Science Tool