Barnstormers is an arcade racing game in the vein of Mario Kart (but with flying aircraft), that was in development by 989 Studios in 1998, for the original Playstation. The project was later cancelled for unknown reasons, but you can still check some target renders in the gallery below.
Thanks to Hey Hey for the contribution! Some more concept art for racing tracks were archived from Concept Art Org
H2Overdrive is a cancelled powerboat racing game developed by VisiWare, that was going to be published in 2001 on the Playstation 2 by Crave Entertainment. In the game players would have been able to race in the fictional Global Powerboat Racers League, which features events set in locations ranging from rivers and lakes to the surface of the planet Mars, with 7 modes of play: championship, simple race, duel, survival, checkpoint, ghost, and cat and mouse. The project was never released, maybe because of some problems with the publisher or for quality reasons.
This game is not related to the arcade-only H2Overdrive, developed by the guys who made the original Hydro Thunder.
Motocross Challenge is a racing game somehow similar to Excitebike that was in development by DHG Games for the Nintendo DS. The project originally started as a Gameboy Advance game, but after Motocross Challenge GBA was cancelled, it evolved into a DS game that should have been released in 2009. After some months the official DHG Games website went down without any explanations and the DS version was cancelled too. As the developers shared the GBA version online to let the fans to play it even if it was never published, it could be possible that in the future they will leak the DS version too.
Set in a post-apocalyptic environment, the original Powerslide was a racing game developed by Ratbag Games and released for the PC on December 1998. In 2003 Ratbag were working on a (self-funded) sequel, know as Powerslide: Slipstream, but the project was canceled because they were not able to find a publisher interested in the game.
As we can read in the original press release, “Powerslide: Slipstream featured drive-anywhere environments full of jumps and action across twelve post-apocalyptic environments, including Berlin, Los Angeles, London and Sydney. Wheel-to-wheel collisions promise spectacular accidents, with special animated features on the vehicles, including moving fins and stream vents for slipstream mode.”