What are the followers of Muslim called?

Muslim. In older books, you'll see them called "Mohammedans" or "Musselmen" or "Saracens" (which actually means Arabs, or people who live in tents), but Muslim is now the preferred term.

Muslims object to being called Mohammedans because they see in that a parallel to the followers of Christ being called Christians, and since Christians hold that Christ was divine, Muslims think that Christians think that THEY think Mohammed was also divine, which he wasn't. (This is a little convoluted, but the upshot is they want to distinguish their belief in Mohammed from the Christian's belief in Christ.)

One could argue that lots of groups are called after their founders without any implication of divinity -- for example, some Democrats are called "Jeffersonians" -- so Muslims certainly are Mohammedans in the political sense, but it's usually best to call people whatever they like to be called.