@shauna lools like the signal suggestions are covered.
https://github.com/Gedsh/InviZible is an excellent privacy tool, only for android.
@torproject browser is both ios and droid, and should be on every phone.
@getgrid is a cross platform privacy focused live location sharing app. It's under heavy development(maybe alpha/beta) and doesn't always work me.
There's a lot of "more advanced" privacy projects, but these are all ones you could learn easily and teach quickly.
If you want more ideas...