Ask HN: How can a web app operate on user-held data?
LocalStorage or IndexedDB on the client-side, with Javascript.  The &quot;untrusted&quot; aspect is not a significant concern, since both browser JS and these APIs are sandboxed and can&#x27;t escape a single file associated with the website.  CPU usage and disk storage can be a concern, but most non-abusive sites won&#x27;t be anywhere close to hitting levels where the user cares.<p>The biggest problem is that <i>a lot</i> of the algorithms that made the web successful can&#x27;t be run on just one person&#x27;s data.  There&#x27;s a reason why webapps replaced desktop apps, and that reason isn&#x27;t <i>just</i> that you only need a single UI with no installation and aren&#x27;t vulnerable to all the Windows worms that were going around in the early 2000s.  If you try to compete with leading webapps you quickly realize the extent to which collecting all that data actually helps them build better products.