Slideshow

Amongst your switches at Admin Panel -> Settings -> Switches you have two slideshow options: "Forum slideshow" and "Topic image slideshow". The former enables a link in the forum actions menu where everyone can view a slideshow all the images uploaded to topics in the forum. The latter is for the topic details page and makes the thumbnails of any images attached to the topic open in a slideshow when clicked.

In both cases the slideshows use lightbox, which is a common javascript slideshow which overlays on top of the page graying out the background, with arrows for navigation and a close button. The slideshow images are in templates/images_default and are defined here in the stylesheet:

.lb-prev:hover { background-image: url('../images_default/lightbox-prev.png'); }
.lb-next:hover { background-image: url('../images_default/lightbox-next.png'); }
.lb-data .lb-close { background-image: url('../images_default/lightbox-close.png'); }
.lb-cancel { background-image: url('../images_default/lightbox-loading.gif'); }