[cheesegrits]

That's going to need customizing your site for each "thing" you want to control access to. What kind of customizing you need to do will depend on what the "thing" is. It might be as simple as template conditionals using is_member_of($userinfo,$goupid), and/or plugins in the "thing" to prevent them sidestepping the navbar link and going straight to a URL.

So say you have your Arcade link in the navbar, and your promotion groupw that let them play Arcade have the iD's of 27 and 32, you'd wrap this round your Arcade link ...

<if condition="is_member_of($userinfo['userid'],27,32)">
... link to Arcade ...
</if>

Then to prevent them simply typing the arcade.php (or whatever it is) link in directly, you'd need to hang a plugin on the first available hook in arcade.php, and do a similar test in PHP, and throw a polite error if they aren't in the appropriate groups.

I think this will work, although I have some nagging memory telling me that promotional groups may not work the same when it comes to is_member_of().

Either way, AFAIK, there is no generic mod which lets you do this. You'll have to roll your own set of customizations to achieve it.

-- hugh