Belief that all souls will be saved is called universalism, and sometimes apocastasis; belief that souls in hell will be destroyed utterly is annihilationism. In Christianity, few denominations preach either as an article of faith. The Unitarian Universalists and the Unity Church are, of course, universalists; Mormons believe hell is temporary and all except the really bad people get out (the latter being thrown into the Outer Darkness); Seventh-Day Adventists and Jehovah’s Witnesses, among others, are annihilationists.
Some Christians who are members of denominations that do preach eternal torment can’t reconcile it with the idea of an all-merciful or all-loving God, and adopt a universalist outlook; it isn’t what their religion actually says, though.
Universalism is a big part of some other religions, though; Hinduism and Buddhism preach reincarnation until one attains nirvana, and Zoroastrianism teaches that although there is a particular judgment, it is not final.
