Update []:
JNMartin's unofficial Dreamcast port of Mario Kart 64 is now available to play, as spotted by VideoGameEsoterica yesterday.
Most of the files you need to compile the game are available on the project's GitHub page (along with instructions). Though, as always, you'll also need to acquire a Mario Kart 64 ROM of the game yourself in Z64 format to supply the game's assets.
Interestingly, one thing we noticed is that it appears that the character Toad is still in this version of the game. That's despite prior claims that he would be replaced by Sonic in the final port.
Original Story: A port of Mario Kart 64 to the Dreamcast is currently in development, from JNMartin — the same person who previously brought WipEout and DOOM 64 to the Sega console.
The news was shared over the weekend by Falco Girgis, a member of the Sega Dreamcast homebrew community, who posted some "very early direct hardware capture" of the classic Nintendo kart racer running on the Sega machine.
As he states, the footage represents "just 3 weeks" of progress, so "there are all kinds of visual glitches and rendering artifacts, the framerate is all over the place, and there's no audio yet...". But this, he claims, is pretty typical for "any ambitious Dreamcast port in the early stages", and will no doubt improve in the future.
To give an example, just a few days ago, the Dreamcast build wouldn't even get past the menu screen, but now it's possible to play every level with multiplayer support enabled.
The port is possible thanks to the Mario Kart 64 decompilation project, which was successfully decompiled a while ago but was recently updated last month to match every function "byte for byte".
More updates on this project are expected in the future. So we'll keep an eye out for them as they emerge.