Who said slides should be rectangles that parade across your screen, one by one? Not Edward Tufte, who mocked Powerpoint's mechanism.
Enter Impress.js, an open source version of the commercial package Prezi. You don't create rectangles; you put all of your message on a big canvas and the software scrolls, rotates, and zooms in on the parts, one by one. The zooming offers a natural way to express high-level abstractions and low-level details. Available under either the MIT or GPL.