gifweasel

gifweasel is a fun little Mac OS X utility we put together to handle a common web developer's task: converting an image to the GIF image format and making parts of the image's background transparent.
Now of course you can do these things with most graphics applications -- applications that take a while to load and learn, cost money, and most importantly, do not have any weasels.

Here then enters gifweasel. It's lightweight, it's free, it's easy to use, and yes, there is a weasel.

You can also visit gifweasel's cousin, pngweasel, for your PNG image transparency editing needs.