The first design was a one man boat, aka the boat-cloak, made of macintosh india-rubber cloth. When deflated the boat could be worn as a waterproof cloak, the oar became a walking stick, and the sail could be used as an umbrella.
Halkett later designed a larger two-man version that folded into a knapsack. Similar to the first design it had multiple uses. When deflated the boat served as a waterproof blanket to allow the users to camp on wet ground. Unfortunately, the boat-cloak was never commercially successful and there's only one original Halkett boat left in existence.
Fast forward to the 21st century and the "packraft" is really making waves with the outdoors/adventure crowd. Check out the product line by Alpacka rafts and you will see some striking similarities. I know my future includes owning a packraft!