Odin application is leaked program for flash official Samsung Firmware or custom root kernel (Latest tutorial how to root Samsung Galaxy S3) into your galaxy s3. Other than Odin, alternative application such as Odin Mobile Pro and Heimdall tools. You can refer link here to get the info and tutorial how to use Mobile Odin Pro for your Galaxy S3. Then what is Heimdall tool ?
Heimdall is a free tool suite used to flash firmware onto Samsung Android devices. The way to use Heimdall to flash firmware or kernel (root) into Samsung Android devices is almost same to Odin, and use the same protocol as Odin to interact with a device in download mode. Compare to Odin, Heimdall not only full support or can install into Windows OS, but also Mac OS and Linux OS. You can download Heimdall for Mac version and install into your Mac (OS X Mountain Lion) OS computer and to flash the firmware into your Samsung Android devices.
How to use Heimdall tool root Samsung Galaxy S3 via Mac OS?
Heimdall is your friend, respect it. But if used improperly it can brick a device since it has the ability to flash very vulnerable sections of your device. At the moment we still not use the Heimdall to root or flash firmware into Galaxy S3 because the latest version of Heimdall, Heimdall Suite 1.3.2 still cant support Samsung Galaxy S3. May be you can consider to use Mobile Odin Pro to flash firmware or kernel directly on you Galaxy S3 phone. You can refer to the Heimdall suite tool developer link to get more info.
Ok, that’s is about alternative tool for flash custom firmware into Galaxy S3. The latest Odin, Odin version V3.07 is available for download. Here is the download Link:
Desktop Odin V3.07 : Link
You can refer here to download Galaxy S3 stock firmware and learn how to flash stock firmware via Desktop Odin: Link