Urban acid for the Gimp
“urban acid” is a popular Photoshop plugin by Steve Almas, circa 2005 [src] that creates a bright, saturated effect [examples] that some Gimp users are trying to reproduce. [discussion]
There are a few ways to do this.
There’s an urban-acid plugin in the GIMP registry that simulates a kind of bright, cross-processed effect. Another GIMP script tries more to emulate the Photoshop effect of the same name. [src]
You can also reproduce the effect by going through the various steps outlined in swobodin’s tutorial on Flickr, which does not require installing any new plug-ins.
Search for more attempts at doing “urban acid” in the Gimp.