Following are a few websites that connect hosts with travelers. Participation is free and rules are informal. Note that overnight stays are not always required. Sometimes people meet simply to share insider tips on a destination.
The Couch Surfing Project
www.couchsurfing.com
Probably the most sophisticated of the bunch. Maps show locations of the fellow surfers who can vouch for the user and countries visited. Three levels of security, plus trackable locations of each person who logs onto the site.
Globalfeeloaders