While not a new idea, AirBed & Breakfast is a fun approach to couch surfing--a time honored tradition that encourages resource sharing between travelers who need a place to stay for a night or two, and people with open couches or a spare room.
The tool is set up like a hotel booking service, allowing people in need of a place to stay an easy way to browse open accommodations by city. As a host you can have people in your house as long as you'd like and set a fee per night or for a specific amount of time. The site also lets you post pictures, list amenities, and note all the little important things like pets, smoking, and whether you'll have a meal ready in the morning (part of the "breakfast" in the moniker).
The service is making its cash by charging a $5 booking fee per night. Otherwise, the rest of the money goes straight to the host and goes through an online payment system so there's no need to deal with cash or check transactions in person. The site was started by a couple of San Francisco locals who took advantage of so many conferences taking place in the area and the need of local conference goers for one or two days' lodging.