What are some alternatives?
ImageOptim - Faster web pages and apps.
JPEGmini - JPEGmini - The Photo Optimization Tool Trusted by Tens of Thousands Image Perfectionists
pngquant - command-line utility and library for lossy compression of PNG images
WP Smush - Reduce image file sizes, improve performance and boost your SEO using the free WPMU DEV WordPress...
PNGGauntlet - -Combines PNGOUT, OptiPNG, and DeflOpt to create the smallest PNGs
Optimus.io - Lossless image optimization