Upload a 24-bit PNG with alpha transparency and get back an 8-bit PNG also with alpha transparency.
PNGs, alpha transparency and small file sizes are all good. After reading this article, I was inspired to squish all three of them together into a nice, friendly web service. Photoshop can't make 8-bit + alpha PNGs and sometimes you just don't want to open (or don't have) Fireworks so this site fills the gap.
Simon Madine (thingsinjars), Chief Roboticist at the Angry Robot Zombie Factory.