Streamlit is a python library to build data apps. This is similar to observable, and evidence.
With uv, it is easy to see what streamlit looks like -- uv run --with streamlit streamlit hello -- this launches a demo app with a couple different visualization screens.
This is more along the lines of "UI controls that allow you to change the parameters of a chart/visualization" than evidence's "Dynamic report" approach.
Streamlit is a pythonic middle ground between reporting oriented evidence and a very visualization oriented observable.
another way to look at these three: streamlit is python, observable is javascript, and evidence is sql.