I can not run Xcode 7.0.1 on my MacBook Pro (Retina, 13-inch, Late 2013, 4GB of RAM, 128GB SSD, 20+GB of free space, OSX 10.10.5). I downloaded the DMG file from Apple, and can run it on my Mac mini (Late 2012, 16GB of RAM, 1TB HDD, 200+GB of free space, OSX 10.10.5), but can not run it on my MacBook. The DMG file seems intact and I can browse the contents of Xcode.app; it is seamlessly copied to
/Applications folder. There is no error code or whatsoever, except the phrase "The application "Xcode" can't be opened."
Xcode 6.0.1 runs perfectly on my MacBook.
I tail ed
/var/system/system.log as patrix suggested and here's an interesting line:
kernel: exec of /Applications/Xcode.app/Contents/MaxOS/Xcode denied since it was quarantined by Microsoft\x20Remote\x20Desktop and created without user consent, qtn-flags was 0x00000006