If wish to open wikis or discussion groups up to the public at large, you can choose whether give access to anonymous users or require registration. These registered users are called community users. They can participate in discussion groups or wikis but they cannot access bugs or cases in any way.
Community users require email verification but do not require a license. They provide a way to allow non-FogBugz users access to certain wikis and discussion groups but not others. The access level can be configured for each. For information on running community wikis and setting fine-grained permissions, see Managing a community wiki.
In addition, community users can be given permission to submit bugs to certain projects, and are allowed to download and install the screenshot tool, allowing them to submit cases that include screenshots.
To turn on the community user feature, go to Admin | Site, then the Authentication tab. You can also set whether community users must be created by a FogBugz administrator or they can self-register. See "New User Control" in the Authentication article.