Well, both consist of air-filled chambers to support the fisherman, and are propelled primarily by swim fins. Most anglers wear waders, although some guys go without in the warmer summer months. However, beyond that, there are some significant differences:

Float tubes originated as basically an inner tube with a seat slung through the middle. There are also 'u-boat' shapes, which allow easier entry & exit than a round tube. Those are basically your two primary forms of 'float tubes.' The user is generally submerged to just above the waist, in most cases, although there are some more 'hybrid' craft that have seats a little higher up.

A *kickboat* is a catamaran-type craft, with two inflatable pontoons that support a rack that keeps the seat several inches above water level, in most cases. Again, there are some hybrid rigs that might seat you a little lower. Many kickboats also have oars, which greatly extend your range on a given body of water, as compared to a tube.


Here's a photo of a 'u-boat':

http://www.calfishing.com/dc/user_files/2851.jpg


Here's a kickboat:

http://www.calfishing.com/dc/user_files/2852.jpg