eventlog is a simple app that provides an easy and clean interface for logging diagnostic as well as business intelligence data about activity that occurs in your site.
There is optional Pusher (http://pusher.com) support baked in so that if you add a PUSHER_CONFIG to settings, your events will also be sent to Pusher as well as your database. Using this feature you can write a simple Pusher client to aggregate activity across multiple sites in a dashboard showing live activity.
Out of the box using this does write to the database (and if Pusher is enabled, write to an http connection). For small sites, it should be good enough to use inline but you might at some point want to consider wrapping calls to the log() method and queue them in a job manager like celery or pyres so that the calls become asyncronous.