Not strictly apps, but the cheap borescopes that you can get now (under $25) that plug into an android phone are great when the need arises. Same for the small USB microscopes and vehicle OBD readers if you like to work on your cars. They don't cost much and are very handy problem solvers from time to time.
I use an Iphone for most actual phone stuff but have an orphaned Android phone (not activated on cell but works fine on wifi) just for doing shop stuff.