Spelunky is an open-source, procedurally generated, 2D roguelike platformer where you make your way through endless caves, all while trying to collect treasure and destroy enemies, without dying.
Pro Quick sessions so you can play in short bursts
Being that Spelunky is at its heart a roguelike the gameplay sessions can tend to be quick as the player will die quite often. This makes for something that can be played in quick bursts throughout the day. The convenient saving also lends to this as a game that is still ongoing can be quickly saved in order to be picked up at a later time.