iOS apps:

Fantastical

Threema

Overcast

Prowl (server notifications)

iPeng (for Squeezebox music player)

BrainWave (binaural beats)

Yamaha Chord Tracker (turns MP3s into music charts)

iStroboSoft (high precision guitar tuner)

I tend to be very conservative with purchasing apps on my phone, but these are ones I’ve ended up with, and no regrets with them.