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?
Personally, the one I found the most interesting us the Tleilaxu. They have evolved into truly alien entities, with sinister intentions and very dubious ethics that seem to make perfect sense to them. Through developments like gholas and axolotl tanks, they touch on the concept of using technology for very disturbing goals where the means justify the ends (in their opinions). I feel like they are a dark reflection on actual, real life humans. The Harkonnens are the obvious villains early in the story. But the Tleilaxu are in many ways more dangerous and insidious, but in a more subtle way.