Compress png, jpeg, gif and svg up to 90% with Compressor.io
What a fantastic tool: Compressor.io is a totally free service that let you compress png, jpeg, gif or svg files in a lossy OR lossless way, and the results are dramatic! Filesize decreases of 80-90% are quite usual for .png files. Awesome! Just imagine how much you could reduce all your websites when spending some time with the tool! The results are much better than common tools like PNGauntlet by the way.
Test #1: A simple .png with a very low amount of colours and quite large unicoloured areas.
Test #2: A quite big .png with lots of colours and lots of alpha-transparency.
Awesome! An offline tool is in the planning, and there are alternatives on the web, like TinyPNG.com which also comes with an API and a (commercial) Photoshop Plugin.