From the publishers website:
Necromancer Games--D20 Products with "Third Edition Rules, First Edition Feel"
The Revised Third Edition of the world's most popular fantasy roleplaying game is here. Are you a veteran gamer? Do you remember the good old days of fantasy roleplaying? We at Necromancer Games do, and we are committed to producing high-quality products under the D20 System for use with Third Edition but with a "classic" First Edition feel.
From 2019 publisher website:
Necromancer Games was an American publisher of role-playing games. With offices in Seattle, Washington and Coeur d'Alene, Idaho, the company specialized in material for the d20 System, with most of its products being released under the Open Game License of Wizards of the Coast. Now we are back! The company's slogan, "Third Edition Rules, First Edition Feel," alluded to the fact that while its products use the third edition of the Dungeons & Dragons rules system, they strive to mimic the flavor and style found in game's first edition. They produced 57 individual products during the 3E Era. The Necromancer Games logo features a depiction of Orcus. Necromancer Games was founded in 2000 by Clark Peterson and Bill Webb, the same year Wizards of the Coast released the third edition of the Dungeons & Dragons roleplaying game. The company has partnered with several other gaming companies to release various products, including Judges Guild, Kenzer & Company, Malhavoc Press, Reaper Miniatures, Troll Lord Games, and White Wolf Publishing. In August 2000, Necromancer Games released the first OGL/d20 product of all time: The Wizard's Amulet. The adventure won an ENnie in 2001 for Best Free Product. Bill Webb has since cofounded Frog God Games focusing on adventures designed for both the Pathfinder Roleplaying Game and Swords & Wizardry. In June 2012, Necromancer Games was acquired by Frog God Games. Necromancer Games in its current incarnation is focused on supporting the 5th Edition version of the game. With the financial backing and production resources of Frog God Games, Necromancer Games has added new staff and plans to produce high quality gaming material exclusively for this version of the game. Frog God games will continue to focus on Swords and Wizardry and the Pathfinder Roleplaying Game. Necromancer Games content will be compatible with the Lost Lands world setting of Frog God Games, and may incorporate Frog God Games intellectual property into their products.