Help Desk+Dashboard - Culturesmith

When someone signs up, they create a Sign up card...

...that can be changed into a User card:

Some important permissions:

When Anyone can create a Sign up card, links to sign up will appear.
When Anyone can create a User card, each Sign up can be auto-approved with a verification email.
If permission to create a User is restricted, someone with that permission must approve each Sign up by hand.