[derefr]

Sure it is, in the sense that it’s very likely not using any Chrome-specific APIs (Chrome right now has the least exposed extension API surface to regular, non-ChromiumOS extensions) but rather at most being equivalent to an Electron app, where some of the HTML and JS lives and runs on the client rather than on a server. But that HTML and JS still is HTML and JS built for a web-rendering-engine to parse and run, so it should be fully possible to turn this extension into a regular web-app with not very much work. Probably any sufficiently-motivated programmer could do it in a couple of hours, throwing the result in an S3 bucket for anyone to access. (Not sure how well it’d run on other browsers, but we still call regular web-apps where the developers happened to only test it in one specific browser “web interfaces.”)