PngOptimizer

PngOptimizer is a small and portable app that, as the name suggests, is designed to optimize PNG images in order to reduce overall size occupied on the disk. It also offers support for GIF, BMP and TGA formats.
Since there is no setup pack involved, you can put the executable file anywhere on the hard disk and just click it to run.
In addition, you can save PngOptimizer to a USB flash disk or similar storage unit, to be able to run it on any PC easily, without previously installing anything.
What's more, the app does not create new entries in the Windows registry or Start menu, leaving the disk clean after removal.
The interface is represented by a single and simple frame, where you can import images using the drag-and-drop method. The optimization process automatically starts. PngOptimizer does not create new files but overwrites the original ones instead.
Statistics show the original and new size, along with the task time. Batch processing is supported, meaning that you can work with multiple images at the same time.
PngOptimizer finishes optimization jobs rapidly while using low CPU and RAM, so it does not concern the PC's overall performance. We have not come across any issues in our tests, since the app did not freeze, crash or pop up error dialogs. Thanks to the overall simplicity, PngOptimizer can be used by anyone.