Comment by BrunoBernardino

Both use Google and Bing, though not exclusively, and both joined efforts to create the new, independent EUSP index.

Sources for Ecosia indexes/providers: https://en.wikipedia.org/wiki/Ecosia#Ecosia

Sources for Qwant indexes/providers: https://en.wikipedia.org/wiki/Qwant#Development

EUSP: https://www.eu-searchperspective.com