Ah, in that case, there are a lot, we have a pretty long history. I could probably spend ages listing all the different little strains, theological schools, legal schools, Sufi orders (and Sufism as a whole!), all the different manifestations of Islamism, Quranism, Mahdi movements throughout history, the many divergent sects. Instead I will just talk about one I got into a research binge about recently, because I find them the pretty interesting and they're extremely relevant.

The Alawites/Nusayris are the current ruling class in Syria and they're not exactly Shi'i, though they developed from Shia Gnosticism. The Alawaites have a very secretive structure and belief system. Many of the secrets they hold are known only to a select few within the community, and in general Alawites tend not to share their beliefs with those outside the community.

From what we can tell, they have a very syncretic interpretation of Islam, with elements of Christianity, Gnosticism, and neo-Platonism in their din. The gnoscticism aspect, and the secretiveness, is vital - they believe that the material world is an illusion and that the Truths of the world are successively harder and harder to understand, with only a small cadre of trusted secret-keepers being the ones who can handle the truths. They hold discretion and secrecy as extremely high, core values of Islam. Some of their unique beliefs (ones that were secret but leaked to outsiders) include a belief that souls will reincarnate until judgement day, the fact that they celebrate Christmas and have mass, and they even believe in a trinity consisting of the Prophet Muhammad, Ali, and Salman the Persian (one of Muhammad's important sahaba, the companions of the Prophet), and that God reincarnated into humanity on two different occasions - through the Prophet Joshua and through Ali. To an average Muslim this seems downright un-Islamic, but the Alawites take their beliefs seriously, and their concealment protocols is part of a greater cosmological and praxial belief in keeping secrets, being hidden, and remaining insular, in order to survive and avoid genocide. Indeed, being a minority in Syria at the moment, those who identify with this unique divergent culture constitute a diehard core of the current Assad regime's forces, and it's part of the reason why they are continuing to this day - they believe that they are fighting an existential threat to their community, and to their secrets.