Straightforward, highly efficient, Open Source & Free Image Optimization tool for Mac OS X.
Not much use these days, but can be handy when you need to manually upload photos for the web and email. For a real life example, the snapshot above has gone from its original 53kb to just 22kb without visible quality drop.
I came across this app after I found out my address book files has gone from some double digit megabyte to a whopping 170+ mb — after I attempted a Facebook contact sync on my iPhone via the Facebook app. More on this here.
If you happen to have the same Address Book oversize problem, head over to this tumblr post for a quick fix.