Labyrinth Lord (LL) written and edited by Daniel Proctor and published by Goblinoid Games is a pencil and paper fantasy role-playing game which attempts to recreate the "look and feel" of classic era Dungeons & Dragons (D&D) using the Open Game License (OGL) from Wizards of the Coast. It would appear obvious to most persons reading the rule book that LL borrows its inspiration from the 1981 D&D ruleset revision edited by Tom Moldvay. This version, referred to as "b/x" (for Basic/Expert Set) or simply "Moldvay" by its fans, is considered by many old-school gamers to be the most coherent and well written version of the D&D game.
LL seems to have accomplished its apparent aim of recreating the D&D b/x rule set. Any adventure written to be played with Moldvay's D&D can be run using LL with little or no adjustment to the presentation. The material itself is well written and tightly edited, lacking the misspellings and poor grammar many fan offerings contain. The entire rulebook is organized in a logical manner, building from the low level introductory material dealing with beginning adventurers all the way to 20th level. In between are monsters from A to Z, advice for designing and stocking labyrinths, magic items and spells, and more.
Goblinoid Games has also made it known the material contained in the LL rules is available to others with few restrictions, allowing fans and other publishers alike to create their own derivative material for use with the system. This is known in gaming circles as the Open Gaming Movement, a concept gaining in popularity in the RPG movement; particularly among retro-clone gamers. The open game movement is defined as the practice of publishing content through the open content license which grants permission to modify, copy, and redistribute some or all of the content. It became possible to recreate many aspects of D&D with the OGL when Hasbro released the System Reference Document (SRD). To quote the official Wizards of the Coast web site, the SRD is :
. . .a comprehensive toolbox consisting of rules, races, classes, feats, skills, various systems, spells, magic items, and monsters compatible with the d20 System version of Dungeons & Dragons and various other roleplaying games from Wizards of the Coast. You may consider this material Open Game Content under the Open Game License, and may use, modify, and distribute it.
The OGL and SRD, in turn, have lead to LL and other retro-clone games. The term retro-clone was coined by Goblinoid Games to describe its faithful reproductions of Moldvay D&D and other games and has caught on among RPG fans, who now use it to describe the recreation of any out of print and non-supported RPG rules created under the OGL. Besides Labyrinth Lord, other retro-clone RPGs include: OSRIC (1st Edition AD&D), GORE (Call of Cthulhu and RuneQuest), Mutant Future (Gamma World), and BFRPG (D&D).
Labyrinth Lord is available as a free PDF download at the Goblinoid Games  web site, and hardcopy versions of the rules can be purchased from the Lulu Print-On-Demand service in 3 versions: coil bound, perfect bound, and hard bound.