A random collection of notes on the Angstrom builds for Beagleboard
Koen is responsible for the distribution at http://www.angstrom-distribution.org/demo/beagleboard/.
USR0: heartbeat, driven by the Kernel. However, it is possible for the board to fail to boot yet the heartbeat to continue (for instance the "pixel clock problem").
USR1: MMC IO activity monitor.
DSS2 is the display driver that has been virtually rewritten. It includes a sysfs interface at /sys/class/grpahics and /sys/driver/platform/omapdss. See for instance  for more info - or just search the google mailing list for DSS2.
James is an alternative build that is being used for the Beagleboard James project. Some developers say it has better display and devices support than the Koen distribution.