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:

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 of OpenImageIO are hard to find for windows I want to share my "unofficial" 64bit builds for windows. The library has been compiled with /MD. Not all feature are enabled (especially the Python bindings are missing). 

OpenImageIO 1.5.0 without OpenColorIO support

OpenImageIO 1.5.0 with OpenColorIO support