I am currently running Xcode 7.1 on my Mac. I need to support a project that is built in Xcode 6.4 (6e35b). How can I download Xcode 6.4 and be able to use it without having it interfere with my Xcode 7.1 installation?
How can I run Xcode 6 and Xcode 7 on same mac?
Just download xcode 6.4 from the SDK menu. You will see a link for other downloads. I just put mine on the desktop so I wouldn't get it confused with my other installation. Note you have to be running 10.10.5 as xcode 6.4 won't work on 10.11.
You can run both versions side by side if you like, but one of them should be renamed. I'd leave the most current version name as-is so you can update from the MAS. Remember too that they will both boot using the same plist/prefs, so be aware if you have an app you only want to use in one version.