libgallery is a Go library providing an interface for accessing boorus and other sites in a booru-like fashion. It comes with some official drivers built-in. This greatly simplifies writing tools for boorus, and enables some interesting possibilities.
It's currently in very-early development. There will be many breaking changes until the 1.0 release.
Isn't this just Hydrus?
No, it's a Go interface to access resources, whereas Hydrus is a database you can query with tags. It's helpful to think of it like RetroArch but for fetching things, though, it can be used for more than just boorus (you could even write a driver for Hydrus!)
Can I use this from language X?
Currently only Go is supported, but bindings to other languages like Python are something that's being looked into.
Why should I use this?
It makes it so that you don't need to write a bunch of unique code for each booru you want to access, as well as allowing you to access other places as if they were a booru using virtual drivers.