Couch surfing https://www.couchsurfing.com/ (Trade-Free)
https://www.trustroots.org/ (Trade-Free)
https://www.bewelcome.org/ (trade-free)
Find lodging in exchange for helping out on a project:
https://www.volunteersbase.com/
Have a place to stay in exchange for chatting with the host:
https://www.talktalkbnb.com/
WWOOF http://wwoofinternational.org/ (charges for registration)
Workaway https://www.workaway.info
https://github.com/Darnok11/Freelife/blob/master/README.mdFind free lodging while bicycling https://www.warmshowers.org/