Mention your favourite unfamous FOSS privacy-friendly app

As the title says. I guess most of us aware of the famous well known apps and services that respect privacy, e.g. ProtonMail, Linux, Tor, DDG and etc.
But there is other cool usefull apps and alternatives that the majority of people didnt hear of.

For me, there is two apps that i really love:
- Newpipe: A Foss youtube client that could really replace youtube app on your phone instead of the slow web GUI, with some other cool …

alternatives app apps aware etc foss linux people privacy protonmail respect services tor