Valve was once hard at work on a third-person MMORPG called Prospero? Alas, the studio scrapped the project around 1997 in favor of a little tiny game called Half-Life, which "absorbed" the developers working on the MMO.
Website Valve Time has dipped into the mysterious history of the game, said to be a "moody, literary" science-fantasy epic influenced by Myst with its focus on story and exploration. Though Prospero was canceled, some of its groundbreaking social and map features were eventually realized in Steam and Portal.
The video also includes some wonderfully dated screenshots and quotes from developers who worked on the title.