ShortPixel is described as 'image optimization API and WordPress plugin that helps improve your website performance. Both lossy and lossless compression available' and is an app in the Photos & Graphics category. There are more than 25 alternatives to ShortPixel for a variety of platforms, including Online / Web-based, Mac, Windows, Wordpress and Linux. The best alternative is ImageOptim. It's not free, so if you're looking for a free alternative, you could try RIOT - Radical Image Optimization Tool or TinyPNG. Other great apps like ShortPixel are JPEGmini (Paid), Optimage (Freemium), Kraken Web Optimizer (Freemium) and EWWW Image Optimizer (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).
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.
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!
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.
Crunch - Insane(ly slow but wicked good) PNG image optimization. It combines selective bit depth, color type, and color palette reduction with zopfli DEFLATE compression algorithm encoding using embedded versions of the pngquant and zopflipng PNG optimization tools.