Compressor.io is described as 'powerful online tool for reducing drastically the size of your images and photos whilst maintaining a high quality with almost no difference before and after compression' and is an website in the Photos & Graphics category. There are nine alternatives to Compressor.io, not only websites but also apps for Wordpress, Firefox and Google Chrome. The best alternative is EWWW Image Optimizer, which is both free and Open Source. Other great sites and apps similar to Compressor.io are Kraken Web Optimizer (Freemium), WP Smush (Freemium), Imagify (Freemium) and Imagecompressor.io (Free).
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.
WP Smush 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.