Each one warrants a post of its own. So only in short for now:

Credits - your own on-site currency, which can be bought or sold, can be used as payment method in Market or for paid levels.

Badges - special visual identifiers assigned by Admins. Can be used to give “verified” status or as “insignia“ of sorts that isn’t tied to membership levels.

Audit - admin-side actions tracker for reviewing what actions each member has performed.

Wiki - collaborative page and content publishing with Macros.