accounts-testing allows you to test different users in your system before integrating with another accounts system.
$ mrt add accounts-testing
Log in with username. If will be created if it doesn't already exist:
Meteor.insecureUserLogin(username);
Add {{> loginButtons}} to any template to see the currently logged-in user and get the button to logout.
Check out https://github.com/mizzao/meteor-user-status for a cool plugin that keeps track of which users are online. This package is used in the demo at http://user-status.meteor.com.