Volunteer

https://en.wikipedia.org/wiki/Volunteering

Site
http://www.volunteers.org/

International
http://www.isvolunteers.org/
http://volunteerinternational.org/

Global
https://globalvolunteers.org
http://www.globalvolunteernetwork.org/

Match
https://www.volunteermatch.org/

Forever
https://www.volunteerforever.com/
http://everything-voluntary.com

United
http://www.unitedplanet.org/

Hq
https://www.volunteerhq.org/