The Apple Keynote is in fact a presentation software application. It was actually developed as a part of the iWork productivity suite by Apple Inc.
Keynote was at first as a computer program for Apple CEO, the famous Steve Jobs, to use when making his the presentations for Expo, Macworld Conference, and other events. Before Keynote, Jobs had used Concurrence, from Lighthouse Design, a similar product which ran on the NeXTSTEP and OpenStep platforms.
Apple Keynote was first sold publicly under the name "Keynote 1.0" back in 2003. It obviously began immediately to compete against existing presentation softwares. Specially the extremely popular Microsoft PowerPoint.