The first line from Jon’s website seems to sum it up pretty well:

Using mootools v1.11, this javascript gallery and slideshow system allows you to have simple and smooth (cross-fading…) image galleries, slideshows, showcases and other cool stuff on your website…

I’ve been doing a lot of slideshow research to try and find the best one for an artist client. SmoothGallery does look pretty promising.

Rock Web Money!