Hydrus

The hydrus network client is a desktop application written for Anonymous and other internet enthusiasts with large media collections. It organises your files into an internal database and browses them with tags instead of folders, a little like a booru on your desktop. Tags and files can be anonymously shared through custom servers that any user may run. Everything is free, nothing phones home, and the source code is included with the release. It is developed mostly for Windows, but builds for Linux and macOS are available (perhaps with some limitations, depending on your situation).

Currently importable filetypes are:

images - jpg, gif (including animated), png (including animated!), tiff, webp, bmp

video - webm, mp4, mpeg, avi, mov, mkv, flv, wmv

audio - mp3, flac, ogg, wma

misc - swf, pdf, psd, zip, rar, 7z

The client can download files and parse tags from a number of websites, including by default:

various imageboards, with a thread watcher

the popular boorus

gallery sites like deviant art, and pixiv

tumblr and twitter

And can be extended to download from more locations using easily shareable user-made downloaders. It can also be set to 'subscribe' to any gallery search, repeating it every few days to keep up with new results.

The program's emphasis is on your freedom. There is no DRM, no spying, no censorship. The program never phones home.