What are some alternatives?
Atomic - The fastest way to design beautiful interactions
Slides - Slides is a place for creating, presenting and sharing presentations. The Slides editor is available right in your browser. Unlike traditional presentation software, like PowerPoint, there's no need to download anything.
RedMark - Redmark helps graphic designers work better and faster.
FlowVella - How To: E*Value on FlowVella - Presentation Software for Mac iPad and iPhone.
Invision - Prototyping and collaboration for design teams
Powtoon Slides - Impress with elegant design and stunning animated templates