Complex sentence: Oneness Pentecostalism is a specific sect of Pentecostalism, although others who are not Pentecostals also believe in the'oneness' of God: see also Unitarianism, Sabellianism and Nontrinitarianism.
Split into simpler sentences: Oneness Pentecostalism is a specific sect of Pentecostalism proclaiming the Oneness of God. There are others (not Pentecostals) who believe in the Oneness of God: see also Unitarianism, Sabellianism, and Nontrinitarianism.