This is a late reply to Seloco's question about propfans and turboprops - sorry, but the memory banks seem to be on a go-slow ...
I think that the term "propfan" is/was a GE (registered?) name for their engine with rear-mounted contra-rotating propellers. The blades were, to put it crudely, extensions of the "shrouds" of the two contra-rotating power turbine stages, but I don't remember (and haven't got the documentation) that they had a pitch-change mechanism.
While significant SFC advantages were claimed over conventional turbofans, noise was a severe problem (as Shackleton crews will remember from the contraprops on their piston engines) which GE tried to alleviate by varying the number of blades in each bank.
The layout was suitable for rear-engined aircraft like the DC-9 on which it was tested, but the aft-prop layout made wing-mounting a problem - at the time there were some exotic layouts proposed, but there were other ways to get overall efficiency increases and until the price of a barrel of oil went rapidly north-east, the concept was dormant.
A decided advantage over layouts like P&W's Geared Turbo Fan is that there's no gearbox, which gives the Propfan a significant weight advantage. Perhaps with the rear-engined all-wing airframe layouts both Boeing and, much earlier, Aerospatiale have shown, the concept might make a come-back, though those only showed high bypass turbofans ...
