A massive 8-volume monster manual series. The PDFs provide exhaustive details on monster biology, social structures, and even the value of their remains for salvaging. Key Gameplay Mechanics
Because the legal situation is stagnant, a legitimate fan preservation effort exists. The HackMaster International fan group has worked with Kenzer’s permission to create a of the entire 4e line—available only to members who prove they own a physical copy. hackmaster 4e pdf
Kenzer & Company now promotes HackMaster 5th Edition (also called HackMaster Basic Plus or the "new" HackMaster). This game is not compatible with 4e. It uses a completely original d20 + d100 hybrid system. Do not buy 5e PDFs thinking they are 4e content. A massive 8-volume monster manual series