Boorus. Oriented towards media, not text. There are many. Every booru I have seen identifies files by their checksum, usually MD5. It may be better instead to identify them by a perceptual hash.
Hydrus. A cross-platform desktop booru with optional server-based collaboration. Stores tags in a database.
Tabbles. A desktop and Web-based document manager with optional server-based collaboration. Windows-only. Allows chat-like comments on files. Stores tags in a database. Proprietary.
TagSpaces. A cross-platform desktop document manager. Stores tags in filenames or sidecar files.
TMSU. A cross-platform command line tool for tagging files. Can expose a virtual filesystem for accessing files by tag. Stores tags in a database.