Epic Words is tailored to this function for your campaign, but has many features otherwise. It is a freemium service, i.e you get certain functionality for free (which seems like it would cover your needs), but you can pay for more features.
From the about page:
Free Accounts will have access to all of Epic Words original tools
including: blogs, wikis, loot lists, experience tracking, forums, and
private messaging. These users can have up to 3 characters, and run 1
campaign as Game Master.
Paid Accounts are only $12 a year, and include all the features of
free accounts. In addition, paid accounts will let users run up to 10
campaigns, 15 characters, secure dice rolls, AND give them 1GB of
storage space for files. (GM's with Paid Accounts can choose to share
their storage space with players in campaigns they run.)
It has basic privacy controls, with security being able to be set on a per page basis, and being linked to the accounts of the members of the campaign, or to general groups, i.e. yourself, members of the campaign, or public at large.
I really like the abilities of Obsidian Portal better, as they have more advanced layout options and such. But the actual controls built into the campaign are better on the Epic Words site, IMO.
Moving outside of the RPG centric realm, there are a few other hosted options that you might want to take a look at:
Zoho Wiki- is a good option as long as your campaign is small. You get up to 3 users, so only those three are granular as far as permissions go. Everyone else would fall into public. An idea that I've used in those constraints is to set up accounts for groups of users. But it's suboptimal at best.
CloudStore- A bit more involved, but as you noted that you have information that you want to keep, it's a step between using someone else's servers and maintaining your own. Using CloudStore you can use one of the following options:
- Wagn- is a pretty heavy weight option, but it is open source and has a lot of options. It organizes information into cards that can be categorized and permissions assigned granularly to each. I've only used it very lightly; it was more than I was looking for. But it does have the options that you need.
- MediaWiki- also a pretty heavyweight options, with the same benefits and drawbacks of Wagn. It also has the benefit of being in wide distribution, so
