The Injured Personnel Carrier (IPC) was designed to let one person carry another in a way that makes it possible to navigate small corridors, stairs, etc… while keeping both hands available for combat duty. The concept is extremely simple (therefore reliable?) and it basically turns the down solder into a backpack. When used in conjunction with a tactical vest, this could spread the weight over a much larger.
Now, non-combatant rescue personnel like firefighters are jumping on board, as this seems to be an effective way to carry people. Made by Agilite, the IPC costs about $80. Official video below: