With 10,000 hosts in 160 countries, according to the site, the concept of NightSwapping is based on a virtual "Wallet." List your home or a room in your home with a price per night fee. When a person chooses your accommodations, you earn the total of that stay in your "Wallet." You can then use the funds in that wallet to stay at another member's place for free. Or, you can choose to collect the money to go to your bank account.
It's necessary to host in order to gain a free stay somewhere else. If you're not traveling, it's also a way to earn extra money. There's no commission fee if you choose to take the cash.
How to travel free or nearly free this summer