OpenImageIO
Library and Tools for image manipulation
OpenImageIO is a library for reading and writing images, and a bunch of related classes, utilities, and applications. It's home can be found here: https://sites.google.com/site/openimageio/home
More information can be found at the project home website. But I find especially the included tools like maketx, oiiotool and iconvert really really usefull. They are pretty powerfull commandline applications that allow you to do a lot of image conversion and manipulation task from the commandline. And iv is a nice little image viewer.
Since windows binaries and precompiled libraries of OpenImageIO are hard to find for windows I want to share my "unofficial" 64bit builds for windows. The libraries have been compiled with /MD. Not all feature are enabled (especially the Python bindings are missing).
OpenImageIO 1.5.0 without OpenColorIO, VS2010
OpenImageIO 1.5.0 with OpenColorIO, VS2010
The following is a build of the current master (8-2017), not a official release. More of a beta, but seems to work. Build static with /MT
OpenImageIO 1.8.5 without OpenColorIO, VS2015