Pure Skill Minesweeper
I had a co-worker who played minesweeper all day long on his Linux workstation which I had remote access to.  I grabbed the source code for the exact version of gnome-mines he was using and compiled my own version with some back doors.  I would also launch an xvnc server so I could see him playing from my desk.  Sometimes I'd have people over at my desk watching him play.  It was hilarious.I could enable various features while the game was playing.  Features included:
* Always lose on first click
* Always win on first click
* Force a guess in all 4 corners... so even if played perfectly he'd have to make 4 guesses.
* Load custom designs from text file.  For instance I had some that spelled things out.
* Every click would be completely surrounded by mines (i.e. the number 8) until half the mines were exhausted.  This one was fun because I remember him not believing it and actually clicking on a mine.
* Ridiculous sounds when he won or lost