The Boeing 737-700C is an interesting aircraft. What makes it unique is its ability to convert from passengers to cargo depending on how the airline wants to use it.

It's by no means a new model, but you can call yourself lucky to spot it. It evidently has great advantages for the military (the US Naval Reserve calls it the C-40A Clipper) and it has finally made a commercial transition with Air Algerie having just ordered two. 

This is actually a 737-200C, but you get the idea. (photo credit: Alasdair McLellan)