Dblog: Capture system events in log

In Drupal 5.x and earlier, this module is called watchdog.

The dblog module monitors your system, capturing system events in a log to be reviewed by an authorized individual at a later time. This is useful for site administrators who want a quick overview of activities on their site. The logs also record the sequence of events, so it can be useful for debugging site errors.
The dblog log is simply a list of recorded events containing usage data, performance data, errors, warnings and operational information. Administrators should check the dblog report on a regular basis to ensure their site is working properly.