One of the more famous unfinished games on the PlayStation is Resident Evil 1.5, a title that was originally intended to be Resident Evil 2 before it was scrapped at the 11th hour and replaced with, well, Resident Evil 2.
The title's unfinished and mysterious nature has led it to develop a bit of a cult following, and for a little while now a team of fans has—having obtained code of the projcet—been working to restore as much as they could and release a playable build to the public.
Well, after some messy internal politics and alleged hacks, the team has gone out ahead of schedule and, rather than wait to release a "finished" build (including English translations), put out a work-in-progress, which you can download and try out.
Be warned: it's an "unstable mess" that is "in no way representative of the current state" of the actual project that'll be released down the line, but hey, if you can't wait for a more polished experience, one it's hoped you'll be able to play on actual PS1 hardware, you can get in on some hidden gaming history below.
Resident Evil 1.5 [The Horror, via NeoGAF, thanks Dennis!]