ImageAlpha is described as 'GUI for pngnq and pngquant. It allows you to easily generate paletted PNG images with full alpha channel' and is an app in the Photos & Graphics category. There are more than 10 alternatives to ImageAlpha for a variety of platforms, including Mac, Windows, Linux, Online / Web-based and BSD. The best alternative is RIOT - Radical Image Optimization Tool, which is free. Other great apps like ImageAlpha are ImageOptim (Free Personal, Open Source), Optimage (Freemium), Color Quantizer (Free) and Black Bird Image Optimizer (Freemium).
Saving images for web/email/other media with the best compression ratio and quality is a difficult task if you don’t have the right tools. Choosing the right format then choosing the right parameters are the key factors of smaller files.
ImageOptim is excellent for publishing images on the web (easily shrinks images “Saved for Web” in Photoshop). It's useful for making Mac and iPhone/iPad applications smaller (if you configure Xcode to allow better optimization).
Effortlessly compress your images without loss of quality. Aerate offers an industry leading default mode, as well as new fast and extreme presets. Switch between modes quickly using the new compression slider.