Perhaps the closest thing voluntourism has to a one-stop comparison site, it lists more than 2,000 programs spanning over 80 countries, from sea-turtle and wildlife conservation to teaching, healthcare and community development. Travelers can compare projects by destination, activity, price, duration, ratings and reviews and apply through the platform. Its most important distinguishing feature is its emphasis on screening: participating organizations are quality-checked against ethical and social-impact standards. Volunteer World also handles payments and offers customer mediation, flexible reservation changes and refunds if a project cancels. It's especially useful for travelers who haven't yet settled on a particular provider.

Read more in my post 5 of the Top Websites for Voluntourism.