WP Smush is described as 'strips hidden, bulky information from your images, reducing the file size without losing quality. The faster your WordPress site loads, the more Google, Bing, Yahoo and other search engines will like it' and is a Image Optimizer in the Photos & Graphics category. There are more than 25 alternatives to WP Smush for a variety of platforms, including Online / Web-based, Mac, Windows, Wordpress and Linux. The best alternative is RIOT - Radical Image Optimization Tool, which is free. Other great apps like WP Smush are ImageOptim (Free Personal, Open Source), TinyPNG (Freemium), JPEGmini (Paid) and FILEminimizer Pictures (Free).
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).
With Image Optimizer you can losslessly optimize your PNG, JPEG and GIF files and thus save your bandwidth and your users' time! Kraken recompresses images with blazing speed and strips metadata with image quality intact.