There is a big difference between alternate universes and alternate history. Alice fell through the rabbit hole into an alternate universe. Robert Silverberg explored the ramifications of alternate history in Up the Line. One lets you go anywhere from the starting place of the "real" Earth (or whatever planet you started on); the other is bound by the strictures of actual history. These are examples of alternate universes:
- Alice in Wonderland and Through the Looking Glass by Lewis Carroll
- Red Moon, Black Mountain by Joy Chant
- The Dragon and the George by Gordon R. Dickson, and its sequels:
The Dragon Knight
The Dragon and the Djinn
The Dragon on the Border- The Riftwar series by Raymond Feist, which also includes the trilogy written with Janni Wurtz. These two series are interesting in that they examine the war from the POV of the opposing sides:
From the Krondor side:
Magician: Apprentice
Magician: Master
Silverthorn
A Darkness at Sethanon
Prince of the Blood
The King's BuccaneerFrom the Tsurani side:
Daughter of the Empire
Servant of the Empire
Mistress of the Empire- The Broken Citadel, Castledown, and The Great Wheel by Joyce Ballou Gregorian
- The Guardians of the Flame series by Joel Rosenberg, comprising:
The Sleeping Dragon
The Sword and the Chain
The Silver Crown
The Warrior Lives
The Road to Ehvenor- Barbara Hambly's Darwath series, including
The Time of the Dark
Armies of Daylight
The Walls of Air
Mother of Winter
Icefalcon's Quest