MarkShown is a very simple app for quickly creating presentations which can be shown on an external display. Markdown syntax is used to format presentation slides and presenter notes; the presentation slides will show on an AirPlay device or other external display, and the presenter notes will show on the local screen.
Presentation images can be loaded from external links, but they cannot be embedded since markdown is just a text format. Links to external websites can be added to the presenter notes, when clicked they will show on the AirPlay display; scrolling the presenter notes scrolls the webpage shown on the AirPlay display. Also, presentation styling can be changed using CSS.
MarkShow is designed to make creating simple, text-based presentations easy, so it does not currently support slide transitions or any other fancy features. If you need a more powerful presentation tool, then by all means stick with Keynote or even Powerpoint