monloader
monloader is the downloader that feeds monbooru. Give it the URL of a booru post, a pool, a tag search, an artist page or a plain image link, and it fetches the files along with their tags, rating and source, and hands them to monbooru.
The downloading itself is done by gallery-dl, so any site gallery-dl supports works. monloader adds a download queue, turns each site’s tags and ratings into monbooru’s, and ships corrections for the sites it knows well.
It also works the other way round. For an image you already have, monloader can search the boorus by the file’s hash or by image similarity (IQDB, SauceNAO), and optionally a local copy of the Hydrus Public Tag Repository, then bring the tags and sources it finds back into monbooru. See Reverse lookup.
The two apps stay apart on purpose. monbooru holds your files and needs no internet. monloader has internet but never touches your files directly: everything goes through monbooru’s API. Like monbooru, it’s meant for your home network, not the open internet.