BuddyPress.org

Andy moved testbp.org over to standard WP because the majority of new BP users are likely to be standard WP users:

http://testbp.org/activity/p/73263/

You could probably use another test install that other developers have setup such as Marius Ooms (http://sandbox.ywamcloud.com/) or David Cartwright (http://namoo.co.uk/). Though their BP installs might not be running the latest trunk version like testbp.org is.

You could always create your own test environment locally as well!