It’s a special version of the client to watch the upcoming International 2 tournament. You cannot play games with it, but its out-of-beta period should be very soon.
Speaking of the International, it starts tomorrow. First matches are at 9AM PDT.
But actually…
Christmas came early! (Sort of.) One of the teams, MUFC, was unable to play due to travel issues. So the 2 backup teams, Mouz and World Elite, are playing in a best-of-5 showdown about one hour from now, 5:00PM PDT, and the winner will get the last spot in the tournament. You can watch it in the game client.
For those unaware of the International, it is a yearly tournament held by Valve with a $1 million prize for the winning team. Last year, the first International sort of marked the unofficial beginning of the DOTA 2 public beta. The second, held this year August 26th-Sept. 2nd, sort of marks the beginning of DOTA 2’s real release.
You can follow the match results here.