ResizePixel is a free online image editor where simplicity is essential feature. It is designed to crop, resize, flip, rotate and convert images to various formats. The service is mobile-friendly, fast and easy to use.
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
Google Open Source - All of Googles open source projects under a single umbrella
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
Ralpha Image Resizer - High-speed image batch conversion tool
Open Source @IFTTT - A collection of IFTTT OSS projects.