This is an extension that embeds Python in LibreOffice Calc like Python in Excel. Once the extension is installed, pandas, matplotlib, numpy, etc. are also installed, allowing tables to be manipulated as pandas data frames.

The difference with Python in Excel is that it works with Python embedded in LibreOffice. It can be used without external access.

GitHub: Amourspirit/python_libre_pythonista_ext: https://github.com/Amourspirit/python_libre_pythonista_ext

Introducing Python in LibreOffice Calc - YouTube: https://www.youtube.com/watch?v=AQLuSNHhUY4

Does this allow external programs/servers to interact with a workbook (xlsx file)? Or is this just to run more complex calculations inside cell(s)?

There's UNO and there's also openpyxl to interact with workbooks from Python, but both solutions were a bit slow when testing it.

There's a lot of value in having existing workbooks which a lot of businesses already use, and extending them so they can be interacted with or queried from a server. For example to allow further access from a webapp without allowing changes to the entire workbook or hiding the full dataset.