This module generates one-time links in order to give access to a configured page/form. Once the form is successfuly submited, the one-time link is no longer valid. The links can be sent to an email address.
If a configured amount of time has elapsed from creation, the one-time link is automatically (cron) removed from database.
Drupal ships with a user login block, but it's a little heavy for a lot of projects I work on. It includes the login form itself, and that's kind of a pain to style and might not have been considered in the initial design phase of the project. What I often need is just a more simple "Hello [user], Logout" link, or - in the case that user hasn't logged in yet, a simple "Login or Create Account" link.