Fedora development team released  first alfa of fedora 18 codename Spherical Cow this is alfa release but it still has many changes and an awesome freshness

Changes in alfa 18

• Terminals now use 256 Colors .
• Gnome version: 3.6.  Gnome version 2,  revert back options
• integration MATE desktop. For Students
• integration of Sugar learning environment.
•  Fedora packaged Owncloud which brings  to backup and sync your personal data.
• firewalld  default firewall software, replacing iptables.
• Fedora will now discover printers and other mDNS devices.
• Also, a preview of next generation Yum packet manag
•  final release of Samba 4 and possibility to join an Active Directory domain out of the box. .
•  updated D environment, latest Fedora Haskell packages as well as the latest stack of Perl and Python.

official release notes : http://fedoraproject.org/wiki/Fedora_18_Alpha_release_notes

preview page : http://fedoraproject.org/en/get-prerelease

schedule list : http://fedoraproject.org/wiki/Releases/18/Schedule

Direct Downlod link ( 32bit PC) : Download fedora alfa 18 

best way to test is install it inside vm because as known issue anaconda isntaller will format all your disk if you are not manually specifying .

The Anaconda installer for Fedora 18 Alpha will format the entire disk unless custom partitioning is selected. See Bugzilla: #855976.