Conceived in 1999, the 5k competition is a prizeless contest intended to drive web designers to create the best and most functional Web site that uses only 5 kilobytes of data, graphics and all.
The purpose is mainly to eliminate overly-large GIFs and JPEGs from the pages and trim them down to the most basic design elements: bold colors, straight lines, clear text. The graphics used are usually one-pixel-square GIFs that are scaled to larger rectangles as necessary, or HTML tables with background colors to simulate boxy graphics. Any interactivity is provided using very conservative dynamic HTML code; server-side code is verboten.
None of these sites are intended to drive major e-commerce, although some of them are personal homepages for their creators. By and large they're intended as a proof of concept, demonstrating that good and even great design is possible while keeping download times to an absolute minimum. The results, if you're a coder yourself and appreciate the subtleties of optimization, will certainly impress you.
Their homepage, along with the winners from previous competitions, is at http://www.the5k.org/