The Crab Nebula was a nebula remnant of a supernova. It was created by the Uxarieans by detonating a star with their Doomsday Weapon. (TV: Colony in Space) This was believed to have occurred during the Millennium War circa 150 million BC. (PROSE: The Quantum Archangel)
The planet Wengrol was located in the Crab Nebula (PROSE: The Sons of the Crab), as was the planet Tora. (COMIC: The Enlightenment of Ly-Chee the Wise)
During a visit to 1980s Blackpool, the Sixth Doctor said that a replica of the town was being built on the rim of the Crab Nebula, but they had gotten the design concept wrong, as it was being built for a purpose rather than for frivolity. (PROSE: The Nightmare Fair/AUDIO: The Nightmare Fair)
In the 51st century, humanity relocated to the Crab Nebula after Earth was ruined by solar flares. (COMIC: The Keep)
The Tenth Doctor took Grayla to either the Crab Nebula or the Horsehead Nebula. (COMIC: The Whispering Gallery)