What are some alternatives?
Transmit - Transmit is an FTP client for Mac OS X and Mac OS Classic (which is unsupported).
TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
CodeKit - CodeKit allows you to optimize the performance of your website by automatically and efficiently compiling a variety of popular languages.
PNGGauntlet - -Combines PNGOUT, OptiPNG, and DeflOpt to create the smallest PNGs
TotalTerminal - TotalTerminal is a plugin for Terminal. app which provides Quake-style terminal window available on keyboard shortcut.
pngquant - command-line utility and library for lossy compression of PNG images