[QUOTE=ralph124c]
Other Islamic sects: what is the origin of;
-the Alawites ( the Syrian sect, which is the religion of the ruling tribe)
-the Druse (a sect found in Lebanon)
-the Saudi sect Wahabites)
-the Sufi sect
-the Ismailist sect (headed by the Aga Khan)
Do all of these sects regard the others as heretics?
[/QUOTE]
The Alawites are a very heterodox subsect of Ithna’ashari ( or Imami or Twelver ) Shi’ism. Some Shi’a authorities regard them as proper Muslims, Sunni authorities have been more equivocal. They’re pretty idiosyncratic, but still consider themselves Muslims.
The Druse are generally considered a seperate religion, albeit one that is a direct offshoot of Isma’ili Shi’ism, as they accept revealed prophecy that postdates the Qur’an.
Wahabism is rather young ( 18th century ) subsect of Sunni Islam as noted, but it’s not quite unique to Saudi Arabia, being also the main faith in Qatar and part of the UAE. It does have its closest ties to the state in SA. It is by far the most conservative and rigid brand of Islam out there ( though the similarly pedigreed Deobandism can get close ) and is so regarded by most Muslims.
As Polycarp alluded Sufism is NOT a sect per se. Rather it is a philosophical approach, representing the mystical strain in Islam. One can simultaneously ( and always are ) Shi’a or Sunni and a Sufi. Sufis organize themselves into “brotherhoods”, which can be considered very rough analogs to monastic orders. Sufis are everywhere, but will tend to clump some areas more than others. In Iraq Sunni Kurds ( mostly followwing the Shafa’i madhab, or school of jurisprudence ) tend to be heavily penetrated by Sufism ( the Barzanis are hereditary Sufi sheikhs ), while the Sunni Arabs ( mostly following the Hanafi madhab ) are much less so.
Wahabis typically regard Sufism as a heretical innovation in Islam.
Isma’ili are, as Angua noted, identical with the Seveners she describes.
Zaydis or Fivers are yet another Shi’a branch.
The Ibadis of Oman ( and some parts of Africa ) are the last remnants of the THIRD major split in Islam ( with the Sunni and Shi’a ), the Kharijites ( though the Ibadi tend to reject that particular label ).
And so forth and so on - there are numerous subgroups and tossing in the whole slew of Sufi brotherhoods, each with its own philosophy, would be a huge affair ( and certainly beyond me 
).
[QUOTE=Polycarp]
Ali gracefully and humbly permitted the first three Caliphs, who were collateral relatives of Mohammed, to precede him in his rightful position (in their eyes).
[/quote]
Not really relatives at all ( maybe at a sizeable remove, as they were all from the same clan ), except by marriage. Some early Shi’a were of the opinion that any member of Muhammed’s direct family would be acceptable and this group merged into the Sunni mainstream after the Abbasids ( descendents of Muhammed’s uncle, Abbas ) gained the Caliphate. The Ali/Fatima exclusiveness as a definition of Shi’ism therefore postdates 749.
Actually, they’re thick as flies. The term sayyid ( or feminine sayyida ) refers to the descendents of Ali. They are quite numerous and in Shi’a traditions tend to enter the “clergy” in disproportionate numbers ( it’s sorta a family calling with most ). For example most, though not all ( it’s not a requirement ), Grand Ayatollahs in Ithna’ashari Shi’ism are sayyids. Not the same as Sayid on lost by the way 
- his name just means “happy”.
) it has often been as revivalist waves, usually originationg at the fringes of the Islamic world, which result in more distinct Sunni sects.