the testgrid provides a daily build of the latest DEV trunk of OpenSimulator. There is an archive of quite some earlier builds in case the latest version doesn't cut it http://metrotest.hypergrid.org/downloads/MetroTest-Versions/
. There are no special additions made like in the MetroEdition of OS though - those are plain OS-builds with a customized configuration only. You can connect to that grid with other releases too, but you'll have to reconfigure them to use the correct URLs.
Login to the Testgrid seems to be impossible at the moment, the admins will look into that soon