Kunena works perfectly fine with Community Builder so yes you can do that. If by group you mean CB GroupJive Group then yes that's available out of the box with the GJ Forums integration, which generates Kunena categories for groups that are only accessible to group members. If by groups you mean Joomla usergroups then adjusting the access of your Kunena categories should be all that's necessary.
The forums you're on now is Kunena with our own CSS styling.
Is there any other Forums extension that can be integrated with CB?
We don't integrate with any other forum extensions. Mostly because they're not free and we're just not in a position to subscribe to a bunch of extensions to integrate them otherwise we likely would. It however is basically possible to integrate with anything you want using CB Auto Actions to push/pull data. You could even bridge CB with external forum systems if you wanted by doing this.
krileon
