December 2 has the distinction of being the calendar day with the most Space Shuttle launches of any in NASA's history. How many shuttles launched on this day?

There were four shuttle launches on this day - STS-27, STS-35, STS-53 and STS-61 of shuttles Atlantis, Columbia, Discovery and Endeavor respectively.

The Atlantis and Discovery missions carried classified DOD payloads. The Columbia mission conducted astronomical observations. The Endeavor mission was the first Hubble Telescope servicing mission and set a record for most spacewalks during a mission (5).

Image of STS-27 launch from NASA via Wikipedia