LyX is a document processor which acts as a frontend to LaTeX. LyX is mostly used to write articles, reports and books.
LyX can also be used to create presentations (a la Powerpoint or OpenOffice Impress) if a suitable document class is installed (think of a document class as a predefined layout). One example of such a layout is Prosper.
As the documentation for Prosper is difficult to read, I have written my own in PDF format. Here is the LyX file to generate this nice PDF.