P3W-924 was home to Ma'chello, its only apparent inhabitant. The stargate entered an elaborate laboratory that contained many of Ma'chello's inventions, including a life support system, his personality transfer device, and inventions for fighting the Goa'uld. The planet was later re-designated as P3C-599.
Cross Reference: Ma'chello, Ma'chello's Inventions, Personality Transfer Device
Episode Reference: Holiday