Nintendo developed the following game for the Disk System. It was never released, and it was never given a name. The label, however, titles it "Development Disk Card, Vol. 0". This proto is an RPG, turn-based game.

Nintendo's protos come in white disks.

All of Nintendo's Disk System protos came in white disks like the one you see above. Nintendo, of course, made three disk colors: yellow (most common), blue (fax games) and white (protos).

This proto sold on Yahoo! Japan auctions for just under $500 bucks. For an unreleased proto from the 8-bit era, that's not a bad price. But also notice the screenshots below, taken from the auction. They seem to suggest that a dump of this game exists, at least in Japan.