Other users have already explained the technical aspect of PWA (i.e. you can install it and run offline as a desktop app). I just want to add that by offline-first I also mean confidentiality -- your data doesn't leave your device, whether you're offline or not.
It started as a collaboration with https://pypi.org/project/Procpath/. For me as a frontend developer it's an interesting challenge to develop, in fact, a desktop app (with background workers running a database and exchanging data with the main thread and so on) in the form of progressive web app (PWA).
But in general I want to solve a problem: a lot of people know SQL which is actually powerful to wrangle data to prepare it for visualisation and analysis. It can't be simpler than drag-and-dropping a CSV into a browser, producing a result set and consuming it by the visualisation component (now Plotly, but more to come).
Anyway, thank you for a hint.