Hi there,
Gone through and understood all the requirements.
The software is indeed not hard to code, but the issue is it is not possible to create files directly from JavaScript (other than cookies). It is possible to create files from node.js, so if a nodejs solution works for you I am more than happy to work on this - and can finish it within 24h.
If we go with node.js - it doesn't mean internet connection will be reqquired, you can run the node script locally and access it with no internet connection. If needed I am happy to write up a guide for you on how to set up nodejs and how to run and access the app.
Alternatively I could write the software in PHP, which you can also run locally but the web server is somewhat harder to set up, so I suggest node.js.
Regards,
Julijan