It will not be free, so you cannot download it without paying for it.
OS X Mavericks
You will find all the public information about OS X Mavericks here: Apple Releases Developer Preview of OS X Mavericks with 200+ New Features.
We are all users, too, so we don't know anything more about Mavericks than you.
For more information on the features of Mavericks see: Apple - OS X Mavericks.
Mavericks is expected to be released sometime this Fall.