There are so many different kinds. A lot depends on what draws them together. Religion? Politics? Back to the land?
Rules vary. Some require you to put all your wealth into the pot, to be shared equally amongst the community. No one is allowed to be of a status different from anyone else.
Of course, that’s nonsense. There’s usually a charismatic leader in communities like this. They usually start out idealistic, and end up corrupt. Absolute power, you know.
The key to the success of a community like this is that they have rules that are realistic, but serve the purpose of the community. People need to have a say, though, and this can make things problematic, as everyone wants to change things in their way.
Another important thing is what do they do? Do they have a way to earn money as a community, or do people go out into the real world to make money, returning at night?
You might want to look up The Farm. There’s also More. Kripalu is quite instructional as to what can happen with charismatic leaders. Then there’s that place in Northern England, or maybe Scotland—it’s name escapes me. Not sure if it’s intentional community, or adult summer camp. Esalen and Omega fit the adult summer camp model, but they do have other community-building stuff included in their ethos.
A lot of people end up in intentional communities to find themselves. They are looking for a purpose, and these kinds of communities seem to offer meaningful lives. Often people will stay from a few days to a few years, and leave, to lead a more conventional life. A few stick it out for the long term, though.