Provides activity streams like those seen on Facebook, Yammer, and Google+ where users can keep track of recent, interesting activity on the site. It is designed to be easy to use, yet extremely flexible, extensible, and standards-compliant.
Activity messages are recorded using Rules and displayed using Views. There is deep integration with Facebook-style Statuses, Organic Groups, and User Relationships. Radioactivity integration is also provided to sort activity streams by relevancy ("top content") and you can use the Flag module to add "like" buttons to content in the stream.
Unlike the other activity stream modules, the Activity Log stream is dynamic. This means that for example if there is an activity message about a node and the node's title changes, the activity message will be updated to reflect this change. It also means that you can interact with content in the stream by for example commenting on it or "liking" it. Scalability concerns are avoided by intelligently caching rendered messages and selectively flushing specific cache entries when events occur that cause the cache to become outdated.
The ability to regenerate activity messages exists, so you can easily upgrade from other activity modules. Additionally there are very granular settings per activity message that allow specifying where each message should appear, who should be able to see it, and whether (and how) you want to group similar messages. This lets you display group and friend activity in users' streams as well as see messages like "Joe, Jack, and 8 others joined the Drupal group" instead of seeing 10 "user joined the Drupal group" messages. Default Rules are provided, so the module should more or less work out of the box.
Development on this module has basically stopped. There will probably be an upgrade path to the Message module for Drupal 7. There will be no D7 version of this module, but Message provides very similar functionality.
If you are using a version from before beta2 and it is working for you, I recommend sticking with it. There are some changes along the way that can make custom activity message rules created in older versions stop working after upgrading to a newer version.
This module was born out of a desire for one module that really addressed all the major pain points in activity modules. It is useful in many situations. However, it can be a little unwieldy, and over time some limitations have shown themselves (check the issue queue for the remaining ones).
The code for this module is very complicated and that makes it somewhat difficult to answer some questions in the issue queue. As a result the issue queue is not as well attended as it is on my other projects.
The Activity Log Email Digests module sends users daily or weekly email digests that contain recent, relevant site activity. The emails are designed to look like the stream you see from Activity Log on your site. Additionally, the Timeago module lets you use "time ago" dates in cached activity messages, reducing the number of database queries required to display activities on high-traffic sites.