Hi!
Streamlit is great! I especially like the mapbox-integration, and beta_columns and placeholders are very useful.
I have created my first streamlit app, a coordinate transformation app for Namibia using the pyproj library. 
The app can perform coordinate conversions between geographic coordinates (i.e. decimal degrees, degrees/minutes/seconds) and projected coordinates (Namibian Gauss Conform, UTM). It can also do datum transformations between WGS84 and Namibian Schwarzeck datum (currently 3 different transformation parameters to choose from).
Input coordinates can be entered as text/number_input or uploaded as csv-file and are shown on the mapbox-map.
Some background in the surveying/GIS field might be helpful.
Here is the link to the app:
https://share.streamlit.io/sibylleengelhard/schwarzeck-transformation/main/schwarzeck.py
Any feedback is very welcome! 
Sibylle