Some applications that don't need a complex GUI use web browsers as a frontend because they are cross-platform and they come with a bunch of 'free' UI elements like buttons, text boxes, sliders, etc. You can also style things pretty easily with CSS and JS, to a point.
It's a flexible way of writing one-off applications; you can run them locally, remotely, or on someone else's machine in the cloud. One useful example is Tabula[1], a browser-based utility for extracting tabular data from PDFs. As it is often used by journalists and other organizations that don't want to leak the data they are analyzing all over the place, it is easy to run locally instead of uploading files to their website. You just point the browser to 'localhost:port' while the server is running.
It uses Plotly Dash[0] which is a python library for making web apps. Its mostly used for data visualization but this project definitely pushes it harder than anything else I've seen.
