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 Bene Gesserit. I would’ve said the Ixians, but we don’t know that much about them, while Heretics and Chapterhouse give us a lot into the inner workings of the sisterhood, and I liked what I saw.