MTOS is now available from SVN, and the new web site is also available:
http://www.movabletype.org/opensource/
Many more details to follow tomorrow. Right now I am exhausted and need to head to bed. I just wanted to give ProNet the first access to it.
Also, expect MTOS mailing lists to come alive tomorrow as well. It is going to be a busy week that is for sure!
For greater detail on where we are, check here: http://www.movabletype.org/opensource/status.html
I promised myself I would keep this short, but I can't help but take this opportunity to thank a few people... First, every active contributing member of ProNet has had a hand in the release of MTOS, whether they know it or not. The discussions we have had here have played a pivotal role in shaping what MTOS would be and inspired us to make it more then we initially envisioned. Thank you.
Most of all, I want to thank and recognize the entire MT team, especially Brad Choate, Chris Hall, Beau Smith, David David, Mark Paschal and Jim Ramsey. They have put in literally countless hours into this product and have been moving at a speed and pace beyond reason since the beginning of the year when MT 4.0 development began. They have all been strong advocates for and key players on Movable Type's journey to becoming open source and we wouldn't have gotten this far without them. I owe all of them a personal debt of gratitude as a user of this product, and as a colleague I am honored to work with all of them.

Congratulations guys.
Now a question - should we be using these forums as a channel for community help and support ?
No permission to start topics :(
Indeed, cant start any topics either. :(
My apologies for the difficulty in starting topics. I am still trying to figure out the right mixture of permissions and sign-in options - and perhaps work out a bug or two. We will get this worked out. I am sorry.
Getting vague "permission denied" errors. Tried to post this, figured this thread is close enough:
When 4.1 is released, will there be any differences in functionality between MTOS and MT4.1 personal? If so, what are they?
The faq says "In addition, commercial add-ons such at MTES and MTCS are only available for paid commercial licensees.". What do those addons provide? Are there other addons/plugins which will also be omitted from the MTOS release?
Also, why is MTOS being released as GPL2-only?