Optimizilla
Not as good as ShortPixel
Optimizilla is "yet another" online image compressor. It's an easy way to drag and drop 20 images.
It's good, however it doesn't beat the compression done by shortpixel.com. In my test, I compressed the same image using Optimizilla and ShortPixel. Optimizilla was able to compress the image 13% while ShortPixel was able to compress the image by 65%.
Website Description
This online image optimizer uses a smart combination of the best optimization and lossy compression algorithms to shrink JPEG and PNG images to the minimum possible size while keeping the required level of quality.
Upload up to 20 images. Wait for the compression to finish. Click thumbnails in the queue for quality setting. Use the slider to control the compression level and mouse/gestures to compare images.
ShortPixel
I would recommend taking your own test: ShortPixel vs Optimizella.