pngcrush is described as 'Pngcrush is an optimizer for PNG (Portable Network Graphics) files. It can be run from a commandline in an MSDOS window, or from a UNIX or LINUX commandline' and is an app in the OS & Utilities category. There are more than 25 alternatives to pngcrush for a variety of platforms, including Mac, Windows, Linux, Online / Web-based and SaaS. The best alternative is ImageOptim. It's not free, so if you're looking for a free alternative, you could try TinyPNG or PNGGauntlet. Other great apps like pngcrush are pngquant (Free, Open Source), Pingo Web Image Optimizer (Free), OptiPNG (Free, Open Source) and PngOptimizer (Free, Open Source).
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).
TinyPNG uses smart lossy compression techniques to reduce the file size of your PNG files. By selectively decreasing the number of colours in the image, fewer bytes are required to store the data. The effect is nearly invisible but it makes a very large difference in file size!
Experimental, fast Web PNG/JPG optimizer which offer lossless, visually lossless or lossy compression. it performs image reductions over iterations thanks to recursive multi-processing and multithreading systems.
OptiPNG is a command-line PNG optimizer that recompresses image files to a smaller size, without losing any information. This program also converts external formats (BMP, GIF, PNM and TIFF) to optimized PNG, and performs PNG integrity checks and corrections.
PngOptimizer compresses graphics files and removes extra, unnecessary data without affecting quality. It will update PNG files or converting BMP, GIF or TGA files to the PNG format using simple drag-and-drop.