I really like the telephone app. You know—the one that receives incoming audio from people and lets you punch in someone else"s number and call them.
I actually hate that one, but I do like the text one (not the DEFAULT one, though).
I also like Simon Tatham's Puzzles. It's the first nonessential thing I install when I'm setting up pretty much any new device.
Regarding spoiler, I just played the default 8x8 tracks before coming to read . On my phone, I don't know how to use the 'mark' feature, so the default 8x8 is a quick challenge with no marking. On my PC, I usually do the 15x15 tricky.
I also have a list of all the 'loopy' variants on my whiteboard, and work through them, ticking them on the board. When I've done them all, usually about two weeks, then I start over, rubbing out the ticks until they're all unticked again. I like the three dodecagonal puzzles, but the 10x10 hard square is the one I find most difficult from the two pages of non-custom loopy puzzles.
Files.
I mostly listen to hour+ (I think the longest is 8 hour) DJ mixes for music, loading them into a folder and playing them in files is way more effective and efficient on my aging phone than the disaster that is iTunes.
Camera+
The old Camera+ app was free, the new one is a few bucks. It’s like a camera upgrade for your phone, giving much finer controls as well as all manual shooting and macro modes.