Rafts are a configuration of tube chambers and a floor. Catarafts consist of two tubes attached with a frame between them, and are popular among river runners, safety boaters, and fishermen. Because they don't have a floor, they're lighter and more maneuverable than conventional rafts. They can also carry a substantial amount of gear but are more cumbersome for carrying people. You can get a good deal and a good fit by buying a frame from the dealer where you purchase your boat.
Most raft builders offer rowing frames designed around specific-sized tubes.
The same holds true for catarafts. Tub floor boats are less expensive but may restrict where you take your craft. Drop-stitch floors are flat, allowing the boat to slide over rocks, spin and draw sideways easier. Flat floors also tend to be better in tight, technical water and make it easier to rig gear and install foot cups. I-Beam floors feature parallel ridges, are less expensive and improve tracking.