You don’t need any apps, you can do it in your own Mac OS X terminal, you don’t even need to upgrade to Yosemite prior to doing this, you just need to download it beforehand. This guide assumes you have some Terminal knowledge and somewhat understands what are Volumes on your Mac (hint: they’re what Windows calls “Drives”).
I guess not many people will use an actual disk, but an empty USB drive larger than 4 GB will also do. Beware, it will erase your entire drive (the USB one).
After downloading Yosemite throug the Mac App Store, plug an USB drive – it should be a Mac OS X Extended (Journaled) partition, if you’re not sure, use Disk Utility to check it. If not, under Disk Utility, select the USB drive and choose then the “Erase” tab. On the “Format” combo box select the “Mac OS X Extended (Journaled)” option and click on the “Erase” button. Notice the “Name” field under the “Format” option – this is your volume name and will be necessary.
Open your terminal and type the following command:
sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/yosemite --applicationpath /Applications/Install\ OS\ X\ Yosemite.app
If your partition (USB drive) is not named “yosemite” (and there’s a good chance it is not), just replace the “yosemite” on “Volumes/yosemite” whith your actual volume name (the displayed “Name” under “Format” on Disk Utility).
Let me explain a lit bit better what the command does:
sudo: sudo lets you run a command using super user privileges, that’s why when you run the command, it asks you for your password.
/Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia: This tells you want to invoke the “createinstallmedia” command, that is under /Applications/Install OS X Yosemite.app/Contents/Resources directory. This is the utility used to actually create the bootable disk. The forward slashes (“/”) are used because the terminal does not deal well with spaces.
–volume /Volumes/yosemite: This tells the createinstallmedia utility where it should create the bootable disk.
–nointeractions: You could add this switch – it erases the disk without confirmation (dangerous one – just kidding).
That’s it, after you run the command, input your password and confirm that the volume will be erased, wait for it to finish, eject the drive and take it somewhere else to install on another computer.
BTW, that’s what your terminal screen will look like when it is done:
Erasing Disk: 0%... 10%... 20%... 30%...100%... Copying installer files to disk... Copy complete. Making disk bootable... Copying boot files... Copy complete. Done.