GEIGER COUNTER
Geiger Counter is a single-session GMless survival horror RPG in which most of the core characters end up dead at the hands of a deadly menace. There has never been a full, final edition released, but many of the earlier drafts (all linked below) have been thoroughly played and enjoyed by hundreds of people.
GEIGER COUNTER: GAMMA / HUBRIS (2013)
These two related versions, which are tightly focused around an Aliens-inspired premise and have many elements inspired by board games, is closer to how I would design the game nowadays.
GEIGER COUNTER: BETA (2008 beta draft)
This version was released at the Ashcan Front booth at Gen Con 2008.
GEIGER COUNTER: ALPHA (2008 alpha draft)
This version remains the favorite of Ben Robbins, the designer of Microscope (2011), who used to run it fairly regularly at Story Games Seattle.