Combining the critical thinking of a strategy game with incremental level design to ensure portability, Hills of Glory: WWII (for the iPad & iPhone) has the depth to keep you hooked, but can still be played for a matter of minutes during lunch.
Multi Theft Auto (MTA) is an open-source software project that adds full on-line gaming support to Rockstar North's Grand Theft Auto: San Andreas PC game, in which this functionality is not originally found.