It was a game-style database that purported to give users 'unrestricted access' to the X-Files cases.
The 'game' had the premise that you had hacked into a 'highly-classified' secret Government Web site enabling you access to all Mulder and Scully's investigations. It had downloadable content to keep the game up to date, but it was very short-lived as the content updates were not very frequent.
Features are as follows (taken directly from the box cover):
Prowl through dossiers assembled on original characters
Inspect audio-visual evidence such as photographs and video clips
Examine 3-D physical evidence
Spy on private locations with video surveillance
Use the desktop designer to choose screen savers, wallpaper, and more.