There's more Interactive Fiction in the world than there are mad hobos, but Aisle stands out as both an approachable entry point to the form and as a fascinating, deeply affecting experiment in its own right. It's from way back in 1999, so I can't hope to defend against snotty cries of "OLD!", but I'm guessing few of you will have played it. More of you should.
Unlike the spiralling storylines and puzzles of much IF, here you have only one move before the game ends. Each of the accepted commands - and there are several dozen, all of which you'll need to deduct or guess at - leads to a different ending. Not necessarily a resolution, but certainly lending a finality to this particular moment in time:
So what do you do? Buy pasta, think about Gnocchi, try to talk to the woman, take your clothes off, start shouting... Some endings are moving, others tragic, others funny, others lurid, others mysterious. It rewards experimentation, logic, lateral thinking and craziness in equal measure.
Crucially, a number of the less eventful endings provide hints as to your character's backstory, which in turn fill your mind with possibilities as to new actions you could attempt. Hence, Groundhog Day - each attempt you make at the game is informed by the events of the previous one(s). You revert back to exactly the same situation every time, but though the world hasn't changed, your knowledge has - and with that comes an uncanny sense of progress.
The game's available from here, a teeny 120Kb. It's in one of those blasted .z5 formats, so you'll need an Infocom interpreter app if you don't already have one - WinFrotz did the trick for me, and very straightforwardly so. Updated - an in-browser no fuss, no mess version of Aisle can be found here. Thanks, Rook.
Warning: there is a Your when it means to say You're. Otherwise, the writing is elegantly sparse and very often moving.
Big thanks to Joe Martin for the tip-off.