Signal signal.org↗ - Free, open source, completely end-to-end encrypted messaging that lead by a non-profit.
Shelter f-droid.org↗ - Use Android’s built-in “Work Profile” feature to install or clone apps into an isolated space.
Simplex f-droid.org↗ - Like Signal but for the more paranoid. Not as good from a UX perspective so I can’t recommend it to everyone, but definitely just as good if privacy/security is your ultimate requirement.
how does shelter differ from insular - assuming you know. I just haven’t seen that one and am curious
(https://f-droid.org/packages/com.oasisfeng.island.fdroid/)