The Knack Hack provides exactly what the publisher's description says - three concise methods of applying a skills system to The Black Hack. The example classes are taken from BH, and the example knacks etc are therefore fantasy-based. But the methods are applicable to any version or hack of BH. I especially like the information on backgrounds - its an extremely clear, succinct explanation of how to use them and is applicable to any game, not just BH. An very worthwhile supplement.