PC Portal Fans, start your downloading engines now. Fan mod prequel Portal: Prelude is finished and available for download now.
The game offers a glimpse (a longer glimpse than the original game, actually) of the events leading up to GlaDOS' little pecadillo with an extra 8 chapters of aperture-wrangling.
You'll need a copy of Portal, obviously. Other requirements here.
Download Portal: Prelude [PortalPrelude]