It is reputed that early versions of Keynote are very close to the Lighthouse Design Concurrence presentation software, which Apple co-founder Steve Jobs was said to have appreciated greatly in his move from glass slides to the electronic version using NeXTSTEP  (NeXTWORLD).
Themes allow the user to keep consistency in colors and fonts throughout the presentation, including charts, graphs and tables. The user can move from slide to slide with 3D transitions that resemble rolling cubes, flipping pages. Or dissolving transitions that fade one slide into the next. With dual monitor support, the presenter can show the presentation on the projector/monitor and still see his desktop or notes from the laptop. PDF/Quicktime/PowerPoint format export allows the user to distribute their presentation across platforms. Keynote also uses .key files based on XML http://developer.apple.com/technotes/tn2002/tn2067.html.
Sources and References
- Keynote at Apple