I was looking for some viewers that can handle displaying both pictures and PDFs (ideally, PPTs, but I reckon that's asking too much), with transitions (fade in, fade out, etc).
On top of that, I needed a CLI interface (not GUI).
Edit: Ideally I was looking for a single viewer, but if it can't be done then what are the alternatives? Right now, I'm thinking about using fbi for everything (that would include extracting each slide as an image). I don't really like this solution, especially because fbi doesn't really support transitions between each photo (a simple fade-in would suffice).
Edit2: I wanted to make a script that used these viewers, that's why I wanted to avoid GUIs.