Name: libvips
Homepage
Why: I am attempting to use it in a personal programming project. Reasons to be included are its superior performance to that of ImageMagick, or GraphicsMagick (which is broken anyway).
Open Source: Yes
Users: Myself most certainly, maybe a few others. Most likely just other packages.
Tarball: https://github.com/jcupitt/libvips/releases/download/v8.5.8/vips-8.5.8.tar.gz
For what it's worth, I was trying to package it myself, and though it seemed to succeed, the feature I am wanting (SVG rendering scaling specifically) didn't work for me.