-
gnab/remark: A simple, in-browser, markdown-driven slideshow tool.
-
FormidableLabs/spectacle: ReactJS based Presentation Library
-
deckjs/deck: Deck is a markdown driven content presentation system
-
Slides.com: Online UI for creating RevealJS decks (no markdown support yet, but maybe someday)
-
Platon.io: Simple markdown presentations, right in the browser, using remarkjs
-
Swipe: Create Interactive Online Presentations On Any Device
Slideshow (S9) is another one (disclaimer: from my humble self), see http://slideshow-s9.github.io/. If I dare to say it's the only one that lets you use / chose template packs (e.g. s6, bespoke.js, shower.js, impress.js, reveal.js, and so on), see http://slideshow-templates.github.io/ and you can design your own template packs (they are actually just GitHub Pages / Jekyll / Liquid templates) and, thus, work by definition "out-of-the-box" on GitHub with GitHub Pages, for example. Free and open source (public domain, actually).