OS X 10.8 Mountain Lion Developer Preview 1 (Build 12A128p) *BETA* | 3.45 GB OS X Mountain Lion Developer Preview is prerelease software. Do not use this prerelease software in a commercial operating environment or with important data. You should back up all of your data before installing this software and regularly back up data while using the software. You will not be able to upgrade from the Mountain Lion Developer Previews to the final Mountain Lion release.
If an installation of the Mountain Lion Developer Preview fails, try using Disk Utility from the Recovery HD to repair the disk. When installing on an NVDIA machine, moving windows or scrolling while in the install environment may cause the installer to crash.