I am currently developing a site basically from scratch; the only third-party tools I'm using are web development libraries like jQuery and Kohana. This means I have full control over user permissions, even moreso than established web software like phpBB or vBulletin might give.
The – somewhat philosophical – question is: What's the difference between an administrator and a moderator?
I'm generally used to users with administration privileges also having moderator privileges, but of course that doesn't necessarily have to be the case. A strict division of User-Moderator-Admin also isn't the only option; I can definitely have more permission levels or fewer, and any user can have any set of permission levels. (For example, you need User permission to log in, Admin permission to access admin controls, and Moderator permission to access moderator controls. My basic test account on the development site has all three permissions, while the "Anonymous" user account has none.)
While the question generally applies to any website, my specific use-case is a site for Magic: the Gathering card game players building decks for the Commander format. The decks are graded and categorized, and users comment on one-another's decks and get help from one another. The deck grading is crowdsourced to the users, performed manually until a "consensus" is reached, and performed automatically after that.