BIM is an activity module that allows individual students to register RSS/Atom feeds and for teaching staff to manage and mark entires in those feeds.
The original intent was that students would be using their choice of blogging platform to maintain a learning/reflective journal for a course. The initial rationale (detailed somewhat in this paper) was aimed at reducing the workload and increasing the effectiveness of individual student learning journals
BIM was originally released in 2010 for Moodle 1.9, presented at MoodleMoot'AU 2010 and used in a few universities. It's now been ported across to Moodle 2.x and being added to CONTRIB.
This page contains a video based on the MoodleMoot'AU 2010 presentation that gives an overview of how it works.