FreshBooks | drupal.org
FreshBooks is a web based accounting application that makes it easy for you to track the time you spend on projects and invoice your clients. The company behind it is very web savvy and has managed to deliver a well documented, easy to use API for third party integration. This module aims to provide a full integration of the FreshBooks API for use by this and other Drupal modules.
This module was just born on Sept. 9, 2008 and so is under heavy development. To support this module's development and try FreshBooks for yourself, you can signup for a free account and test the functionality of the module as it develops.