I added Python support into my terminal, and then split it out into its own website as a REPL powered by Pyodide. It has autocomplete, expandable objects, syntax highlighting, inline matplotlib charts, and many other features.
While I mainly use it in my terminal to test things in my local environment, I think the online version is pretty neat.
Blog post: https://joel.tools/repl/
REPL: https://python.joel.tools/
Pyodide: https://pyodide.org/en/stable/
