The small jobs around a ZIP to APK conversion
Converting a ZIP to an APK takes minutes; the details around it are what eat an afternoon. The archive has to be zipped with index.html at the root, the pages have to use relative paths, the scripts have to be classic rather than modules, Android wants the icon at seven sizes and a package name in a specific syntax, and every update needs a higher version code. Each is trivial on its own, and each produces a blank screen or a rejected upload when wrong — usually after the wait.
These tools do those jobs one at a time, in your browser. The ZIP is opened with JSZip in memory, images are drawn with the Canvas API, and nothing touches the network — so they work offline and you can drop unreleased projects into them safely.
Prefer to skip the pieces? The ZIP to APK builder takes the archive, checks it, generates the icon set and splash, and returns a signed Android app.