There a bunch of tools in this repository, bundled togethere here because they share code. Two of them ("fbi" and "ida") form the repo name.
So, what is in there?
Motif image viewer, see README.ida
Linux console image viewer. Runs on linux framebuffer devices (thus the name "fbi"). Can also use drm devices.
Linux console pdf viewer. These days it is a standalone app using the the poppler library for pdf rendering.
Originally it started as shell script which ran pdf/ps files through ghostscript to render the pdf into a stack of image files for fbi.
Transform jpeg images, like jpegtran, but unlike jpegtran it also transforms the exif thumbnail images.