The items in this series are fan-created, widely-circulated sourcebooks, intended for use with (primarily) Dungeons & Dragons (Original Edition). These "supplements" follow the enumeration of the official materials, and many of them present themselves as if they were official materials (they are not). Note these products are for different game systems and settings, and by different authors. There is no formal, authoritative process for creating items in this series.
The initial, official items, published by TSR are: