Universal copy - turns your screen into a notepad basically where you can copy any text currently showing on it - super handy for a multitude of things

Twilight - you can set a timer or match it with the sunset/sunrise to redshift your screen to help ease the transition to bedtime by negating the blinding blue screen. I have it set to an hour before I'm supposed to be in bed and love it.

If you have a Samsung: Goodlock - shit let's you customize to your heart's content without the need for a different launcher. Pretty awesome imo for a low barrier entry customized phone setup.

Marco Polo - I use this with my family constantly since we live across the world from each other; it's a short video messaging service where you communicate with short videos and history is kept indefinitely. Like snapchat but no disappearing ability and no ads or influencer shit. They also handle it pretty well when you lose a loved one by preseving their account separate from their phone number as, obviously, they won't have ownership of that anymore. Good dev team who listens to feedback and not owned by a bigger corp afaik.