Dear Esther is a mod built with the Source engine (the same used for Half-Life 2, among other games). While designed in First-Person Shooter format, it is in reality more of a sparse, linear narrative with complete emphasis on the plot. This is a story that you quite literally walk through - nothing is trying to kill you, and there are no puzzles that you must solve to progress. Unless, of course, you count the plot. The remake with improved graphics is available on Steam. The old version can be found here.