There's an unreleased Dreamcast game with a playable near-complete build leaked, called Propeller Arena. It's probably in my friend group's top-4 favorite multiplayer games for the platform, despite not actually having been released. Actually aside from MVC2 (still more fun for us amateurs than MVC3—and kinda looks better?) it might be the most likely game for us to play on the DC, just because the others have newer, better replacements, but I've not seen anything newer that's quite as arcadey and easy-playing as Propeller Arena in its niche (multiplayer propeller aircraft dogfighting, mostly)

I'd argue that Capcom has never made a better looking fighter than MVC2.

I really wish they’re re-release it on a modern console. My DC’s gonna die one of these days and it’s a pain to keep old consoles in service. I’d really rather have it than 3. Which is probably why they don’t—it’d directly compete with the new one.

I think it's technically on ios...

Not anymore. Was for a while (and also other platforms) but hasn’t been purchasable in IIRC several years. Though I’d forgotten it was for a while. Still, aside from iOS even those consoles are old enough that I’m trying to find new platforms for all the games I play in them, so I can get rid of ‘em.

It wasn't too difficult to find, either (I think; untested): https://hiddenpalace.org/Propeller_Arena_(Sep_11,_2001_proto...

Despite the game's concept being entirely arcade-focused that prototype date makes me wonder if the plane focus had anything to do with the cancellation...

Yes, it had - also, iirc, it had a level with the twin towers in NY

Edit: Here's a video of "Tower City": https://youtu.be/HE4W5FbeWds?t=748

To build on this, there are currently unreleased games sitting in collectors' hands and some refuse to dump them as it devalues the game. Dumpers have launched crowd funding campaigns in the past in attempts to purchase these rare games so they can get a physical copy to archive.

These will eventually bitrot and be completely worthless from a historical standpoint.

It happens to non-game products too. Way back during a college internship, there was a third-party vendor that had by far the best algorithm for a hardware product my employer was producing. The product was pretty close to finished, when a former employer of the founder of the vendor sued them under a questionable non-compete contract and claimed that the algorithm was stolen (the company that filed suit had a significantly inferior algorithm based on the hardware product's criteria).

Most of the development had to be scrapped, and a new, non-compete-free team was hired to build a clean room algorithm. There was a firewall inside the company where people on the old team practically couldn't even say hello to the people on the new team. And the new algorithm was decent, but not as good as the original vendor's algorithm.

If you're interested in exploring further, https://www.unseen64.net/ has been cataloguing and writing about lost, cancelled and prototype video games since 2001.

There's actually a book about unreleased games, written by Frank Gasking, just about to come out (taking pre-orders as of today).

Myself and other team members were interviewed by the author, some time back, about one of the unreleased games I worked upon (Chips Challenge, NES).

[I have no affiliation with this publication, apart from being interviewed]

https://www.bitmapbooks.co.uk/products/the-games-that-werent

I watched the video and I think this one is playable but it sure does not look complete, or very much fun.

Not that the published game looks much more fun, but at least there are other cars on the road... https://www.youtube.com/watch?v=EPWzRd5wFqU

Apparently only the qualifying was in 3D, the actual race was in 2D and there weren't even any curves (at least not visible ones, although it looks like the player had to steer from time to time going by some cues which I wasn't able to make out). The race wasn't really challenging either - the player started last, but was able to overtake all opponents in 30 seconds, same after the pitstop... but maybe the image they found was just a debug build, I guess the game would have gone through some more playtesting and fine-tuning if it had been released.

I know of at least one that meets your criteria: https://www.youtube.com/watch?v=KkaR8ZaObO0&feature=emb_titl...