Starting to use Wiki's and startting with Wikka Wiki. Don't know if this is the right one, but "Bluehost.com":http://bluehost.com has it as the first option. They don't have mediawiki which is what Wikipedia uses. This one is OK except that it by default let's anyone register and add content. Here is how to turn that off or rather, you put this in your wikka.config.php there is a parameter in the "wikka.config.php":http://docs.wikkawiki.org/ConfigurationOptions file:
bq. allow_user_registration => '1'
So turning this to zero disallows arbitrary user registration.
You can also look at see who is registered on the AdminUsers page if you an admin as the latest release "18.104.22.168":http://docs.wikkawiki.org/WhatsNew1164 was focused on anti spam and so forth.
The best feature though is "invite code":http://docs.wikkawiki.org/UserRegistrationValidationFramework which means you need a password from the admin to be able to register. The so called invitation code. To set this up, you need to "Enable UR Modules":http://docs.wikkawiki.org/UserRegistrationValidationFramework so you add a line in th wikka.config.php file:
bq. 'UR_validation_modules' => 'URInviteCodeModule',
'UR_InviteCode_password' => 'hello world',