Simon Tatham's Portable Puzzle Collection
If you'd like to play these games on your phone, Chris Boyle packaged them up as a no-networking, ad free, and $0 app for Android! It's on the play store here: https://play.google.com/store/apps/details?id=name.boyle.chr...I think "Untangle" is the game I've put the most time into, though other favorites include "Map" and "Flood".