Short answers, pulled from the story.
Crisis Core: Final Fantasy VII follows Zack Fair, a young member of the elite military force SOLDIER, as he investigates the disappearance of fellow SOLDIERs and uncovers Project G, a secret experiment involving Jenova's cells. The story spans the Shinra-Wutai war through the destruction of Nibelheim, ending just before the events of the original 1997 Final Fantasy VII.
Crisis Core: Final Fantasy VII was developed and published by Square Enix exclusively for the PlayStation Portable. It was released in Japan in 2007 and in North America on the 25th of March 2008.
Crisis Core: Final Fantasy VII sold over 2.1 million units worldwide as of March 2009, with 830,000 of those sales coming from Japan. In its first month of release in the United States in March 2008, it sold 301,600 copies.
Crisis Core: Final Fantasy VII was directed by Hajime Tabata. Tetsuya Nomura served as creative producer and character designer, and Kazushige Nojima developed the game's scenario, which was based on a story he had in mind while working on the original Final Fantasy VII.
The Digital Mind Wave, or DMW, is a slot machine mechanic that runs automatically during combat. Matching three pictures of characters Zack has befriended triggers a Limit Break attack, and lining up the number sequence 777 causes Zack to gain an experience level. Nomura and Kitase included it partly out of enthusiasm for pachinko machines.
Crisis Core: Final Fantasy VII Reunion is a remaster of the original game released on the 13th of December 2022, for Nintendo Switch, PlayStation 4, PlayStation 5, Windows, Xbox One, and Xbox Series X/S. Co-developed with Tose using Unreal Engine 4, it features HD graphics, a newly arranged soundtrack, and full voice acting for all dialogue.