A 9th instrument for free
RSB-Free is a gift. All you have to do to get it is to sign up for an account.
RSB, referring to the paid version, contains 8 different instruments each with total of 6 articulations and an interface with effects and options for modifying the sounds. All instruments also include their own set of presets.
Essentially RSB-Free is a 9th instrument given for free instead of being included in the paid product. It has the exact same features (meaning interface, articulations, effects and presets) as the 8 instruments included in the paid product.
Requires full version of Kontakt 5.5 or newer.