Gameontwikkelaar Crytek is going to be CryEngine 3 available for free for non-commercial use. The free ontwikkelkit will regular updates be provided so as to remain constant to the version that Crytek themselves used.
According to Crytek the sdk is not only suited to mods of existing games, but are all the necessary tools to make an entirely new game from the ground up to build. The sdk is 658MB in size and could be on the site of the CryDev community to be downloaded.