A few days ago, Samsung made the announcement that the international Galaxy SIII(I9300) would not be upgradeable to KitKat(KK). Some XDA developers(devs) have decided that this should not be the case and have joined forces to port over the Galaxy Note 2 (N700) ROM over to the I9300. The main devs of the ROM temporarily nicknamed ArchiPort, are JustArchi and Kryten2k35, other devs such arter97 and forumber2 have also contributed to getting the ROM up and running on the I9300. Some work also had to be done to shrink the base N700 ROM to get it to fit into the I9300 internal storage. This could possibly be one of the reason why Samsung could not update the S3, as it couldn't transfer all features of the Touchwiz aka bloatware onto the I9300.
ArchiPort is very much in alpha stage right now, so certain things like calls and sensors eg proximity and rotate aren't exactly functional. Another aspect which shows how experimental this ROM, is that the kernel cannot be changed, as it is a cross between the N700 and I9300. In short, this ROM is not for the faint-hearted aka the inexperienced, but more for power users who are used to flashing ROMs and are aware of the proper bug reporting procedures via logcat.
For those who would prefer a functional and stable KitKat ROM, the XDA I9300 forum is a good place to start as there are many AOSP(Android Open Source Project a la pure Google) KK ROMs such as OmniRom, SlimKat, Archidroid, Paranoid Android and AOKP to choose from. Do take note that rooting is required before you are able to flash a ROM of your choice. You can check out Alexander's guide to rooting the S3 or XDA itself for steps to rooting. The ROMs mentioned above, are simply a small portion of the available ROMs on XDA, which demonstrates that the I9300 is very much alive and kicking and not dead due to Samsung's RAM requirements. Long live rooting and all hail KitKat!
For the i9300 power users out there, what are your thoughts to your favorite KK ROM?