Per https://duckduckgo.com/duckduckgo-help-pages/results/sources/:
We also maintain our own crawler (DuckDuckBot) and many indexes to support our results. Of course, we have more traditional links and images in our search results too, which we largely source from Bing. Our focus is synthesizing all these sources to create a superior search experience.
Last time I tried Viber, it ran fine on Linux, what issues have you had with it?
Discord also works pretty well, minus the white flashing when scrolling through GIFs for me