The nightly tar balls are tar balls of the current code in CVS HEAD, that means whatever was last committed up to 00:15 hours every night.
It contains what will eventually become OpenACS 4.6, when it's released. OpenACS 4.6 is 4.5 plus lots of fixes. No major overhaul is being done in 4.6. That will happen in 4.7.
-Roberto
