Cancelled Games That Were Later Leaked
Video games that managed to unofficially resurface after cancellation and are available to play in either a finished or unfinished state if you know where to look.
I won't be counting unreleased translations such as Earthbound Beginnings/Mother 1's initially-cancelled localization, or betas/prototypes/etc. for games that did eventually come out.
Additional Notes:
Star Fox 2 - Did see an official release in 2017 built-into the SNES Mini/Classic, mostly-unchanged from the leaked build besides some translation differences, a different logo, unfinished multiplayer mode removed, and some bugfixes.
Half-Life - Only applies to the Dreamcast port.
Baldur's Gate - Only applies to the PlayStation port.
Sonic X-Treme - Only a very early prototype is available, doesn't resemble the version shown at E3 1996 that was intended to be released.
Resident Evil - Only applies to the GameBoy Color version.
SimCity - Only applies to the NES version.
StarCraft: Ghost - Only playable on a modified OG Xbox with additional RAM.