There are many houses and other groups in the novels. The most well-known ones being House Atreides, House Harkonnen, the Bene Gesserit, and the Fremen. But Frank Herbert’s created many other groups in his fictional universe, some of which gradually evolved, and some which just died out.
Which is the one you are most fascinated with? And why do you find them so interesting?
The Fremen are the most interesting in my eyes. It helps that we are introduced to them through the Atreides lens, so everything seems so strange and alien. The way they respect the desert, worms, and water scarcity is hard to imagine for the reader, but becomes internally consistent with how the Fremen operate. In Messiah that breaks down a bit, as the water scarcity foundation is ripped away and the Fremen lose purpose. They’re initially framed in a positive light (freeing Dune from the Harkonnens) but the jihad and religious fanaticism show their ignorance and weakness the following books. Still though they are just AWESOME