At first through some cryptic Famitsu
scans that surfaced a couple of days ago, and now in a more official fashion - by ways of a dedicated
website - a new dungeon crawler RPG set in the
Fate/stay night universe is being announced. Titled
Fate/Extra and currently in the works at the Japanese studio Imageepoch (of
Luminous Arc fame) under Type-Moon's watchful eye, the game is planned for release by publisher Marvelous Entertainment in March 2010.

We aren't offered a whole lot of details about the game's story at this time: odds are it will be set in an alternate reality, though it could still be deeply rooted in Type-Moon's original work in some way. As for the gameplay, the most coherent description I found was over on
IGN.
"You'll be able to select a male or female main character at the start of the game. The character you control is known as a "Master." By forming a contract with a creature known as a "Servant," Masters are able to join a holy war.
Gameplay looks like it mixes the dialogue you'd expect of the game given its digital novel roots, with an action oriented battle system. The game's genre is "dungeon RPG," so this presumably means dungeon crawling."
Famitsu's website
posted some early screenshots and character art for Fate/Extra, and those interested in the development staff can have another look at Zepy's
report. Yep, I think that about covers it.