Roleplaying Games OSRIC Rulebook Converting Systems

The Maximum Mayhem Dungeons™ Series of modules are based on the OSRIC™ System (Old-school System Reference and Index Compilation) which is very similar to the first edition of Advanced Dungeons and Dragons or 1e.

Converting Dark Wizard Modules to D&D 5e: WotC Coversions to 5th Edition PDF

Converting early D&D to Pathfinder Pathfinder OGL Conversion Guide

Converting Stats for use with Savage Worlds:  Converting other RPGs to Savage Worlds

Stat Conversions for DCC:  DCC Quick Monster Stats

Understanding THAC0:  Retro RPG Library - THAC0 Explained