For sites about the earliest period of the history of Islam, from 570 to 660 CE; covers the life of the Prophet Muhammad, and the Four Rightly Guided Caliphs.
At the end of this period, Islam split into Shia, and Sunni; until today, the major divisions within the faith. This period also saw the formation of the first sect, the Kharijites.
The earliest Muslim sect. They were alienated by Ali's acceptance of arbitration with Mu'awiyah in 659 CE after the death of Uthman, the third Caliph; murdered Ali, the fourth Caliph; and remained a thorn in the side of the caliphate until the Abbasid period.
Their rigourous puritanism later inspired the al-Moravids and al-Mohads in north Africa, and also influence modern Islamist groups.
They survive today as the Ibadhi group in Oman and the Maghreb.
This is NOT the place for theological discussions.