Couchsurfing

Couchsurfing (http://www.couchsurfing.org) is a worldwide phenomenon that allows members to meet and stay with other members in more than 238 countries and territories. The group has more than 2 million members, and claims more than 2 million successful experiences of hosting or surfing. Membership is free.
The group attracts mostly young people, but there are also plenty of older members. Members may be hosts or guests, or both. Hosts are able to specify when and how many guests they can accommodate, even whether they prefer male or female guests. As the name implies, hosts do not need to provide a separate room for guests.
Couchsurfing's mission, according to their Website, is to "create inspiring experiences." There are numerous testimonials from members who have enjoyed either hosting or visiting other members.
The economic advantages of this type of organization are obvious, and for those who are very open and trusting it could be a good choice.