S5 (Simple Standards-Based Slide Show System) is an XHTML-based file format for defining slideshows. It was created by Eric A. Meyer as an alternative to the browser-centric Opera Show Format. S5 is not a presentation program, but fulfills the same purpose in combination with a standards-compliant web browser.

The initial version of S5^[1][2] was released by Eric Meyer on October 18, 2004 under a Creative Commons license.^[3] With the release of version 1.1 on July 28, 2005, S5 was placed in the public domain.^[1]

On July 17, 2006, Ryan King launched s5project.org, "a new community site, dedicated to the S5 Presentation software".^[4][5][6][7]

On December 4, 2006, Andreas Gohr announced a DokuWiki plugin that converts Wiki markup to XHTML-compatible S5 presentations.^[8]

The content of an S5 presentation can be stored in a single XHTML file. This file contains several slides which are structured in the following way:

<div class="slide">
 <h1>slide title</h1>
 <ul>
   <li>the first point</li>
   <li>the second point</li>
   <li>the third point</li>
 </ul>
 <div class="handout">
  ... additional material that appears
     on the handout
 </div>
</div>

S5 presentations can be viewed in outline and slideshow mode; Cascading Style Sheets are used to define different layouts for outline, slideshow and print. Navigation controls, a dynamically generated list of slides and accesskeys allow browsing back and forth.

A more semantic version of the S5 format is based on the XOXO microformat and uses <li class="slide"> instead of divs for the slides, as well as <ol class="xoxo presentation"> instead of a div for the overall presentation.

• Web-based slideshow