There are myriad quantum possibilities, whole universes existing just a molecular vibration away from our own, worlds where things are very different and others where they're almost the same. In what we call "Whoniverse-B", the Doctor's adventures are just a touch different...
In Whoniverse-B, the 1st Doctor fought the Zarbi on Earth, where the Animus was breeding them.
The 4th Doctor could use his respiratory bypass system to give himself short bursts of super-strength. The Ogri ended up on the wrong end of his powers.
As as symbol of his regeneration trauma, the 6th Doctor spent his first story with a coat that was half-5th and half-6th.
The Whonivere-B's 8th Doctor chose his companions differently, and so did the Master (who also possessed a completely different man).
And of course, you'll all remember how the 10th Doctor's showdown with the Sycorax took place on a beach in Wales.
We have sent our probes into the rift and information is pouring out continually. Stay tuned for more reports from Whoniverse-B!