Hospitality exchange
Hospitality exchange is probably as old as humanity. It's part of muslim culture. In the 20th century Servas was probably the first organized way for exchanging hospitality. In the late 20th century several online hospitality exchange networks popping up:
- bewelcome.org (a fork of Hospitalityclub, free software)
- couchsurfing.org - biggest network, some minor controversies (501(c)3 status, organizational transparency)
- hospitalityclub.org (quite controversial)
- belodged.com
- hospitalityguide.net - overview of hospitality exchange networks
Home exchange or house swapping is a similar concept.