Trigun: The Planet Gunsmoke (lost build of cancelled manga-based PlayStation 2 game; 2002)
Premiering on March 2002 at Sega's GameJam event was a 20 second teaser trailer for an upcoming game based on the Trigun manga series, titled Trigun: The Planet Gunsmoke. The game was being developed for the PlayStation 2 by Red Entertainment, and was to be published by Sega, but it was never released. No explanation has ever been given, with Sega issuing a "no comment" on the current status of the game.
It is widely spculated that Red Entertainment's 2002 PlayStation 2 game Gungrave (which was released in Japan 4 months after that year's GameJam event) is actually a modified version of their Trigun game following it's apparent cancellation. Additionally, there are similarities between the Trigun universe and Gungrave that seem to back this theory up, although it has never been confirmed nor denied by any of the game's developers.
Whether this speculation is true or not, the original game was never released, and it's unknown if much progress was made on the game in the first place.