The Witcher series developer, CD Projekt Red, is offering a free tool set called Redkit which will let modders create non-linear RPGs such as CD Projekt Red's own The Witcher 2: Assassins of Kings (shown).

Redkit has just entered the open beta phase, and will let users take advantage of the game's assets or import their own, use a day/night cycle, determine NPC's interactions with the character, place cameras during dialog cutscenes, and more.

Head over to the Redkit official site for further information.