The BeagleBone can run many different distributions similar to those available for desktops and laptops. However, the BeagleBone is shipped with two specific distributions, namely, Angström and Debian. Both the flavors are available in an easy-to-load format specifically for the BeagleBone.
Angström has supported every Beagle board available since the beginning. The BeagleBone White is shipped with a microSD card that contains Angström. Early revisions of the BeagleBone Black were shipped pre-installed with the Angström. A quick overview of Angström (http://www.angstrom-distribution.org/) is as follows:
Angström is built with OpenEmbedded and provides a lot of configuration flexibility
Angström is more commonly used with embedded devices and is a little bit different from what people might be used to on the desktop/laptop
The entire image can be locally built to give you an image with all the specific sources used in the image