> but trying to save data required hosting it somewhere
With the File System Access API, webpages nowadays can read and write local files just like desktop applications:
https://developer.chrome.com/docs/capabilities/web-apis/file...
Try this text editor for example:
https://googlechromelabs.github.io/text-editor/
It works nicely on Desktop and Mobile.
My dream is that you could write to Google Drive or iCloud Drive transparently too if the browser allows you to
Even better how about a fully functional VSCode: https://vscode.dev
The File System Access API makes it possible.
*In Chrome.