P.S. Detailed review coming up later.
Update: Check out my Visual Tour of Opera 10.5 for more information about this build. In the meantime Opera has officially responded:
There are some reports about an old internal build of 10.5 being available. Don’t run it, the official build on Tuesday is much better and you don’t risk getting nasty trojans on you pc.
If this build is quite old then there is still hope Carakan may make it to pre-alpha.