Playing in the 70's

Getting in the mindset for very old fantasy campaigns.

Gygaxian Style	Arnesonian Style
Game Rules PDFs of the booklets, I don't recommend actually buying this. Much better options below. Fantastic Medieval Campaigns, a faithful recreation of the original text. Delving Deeper, a re-edited (and slightly clarified) retroclone. Swords and Wizardry Complete, a pretty fleshed-out retroclone with numerous modifications. White Box: Fantastic Medieval Adventure Game, a streamlined retroclone with numerous pain points and tables condensed into even a single number, sometimes.	Game Rules Arneson Gaming Sword & Backpack Oldham Rules
Long-form Wisdom Philotomy's Musings, which discusses the common objections to OD&D, and how to make sense of what the game rules mean. Muster, which discusses the player expectations and referee guidance on running OD&D (or similar rulesets) as a fantasy wargame (as was intended!). Musings & Commentary What We Mean When We Say “Encounter”, understanding how to interpret the rolls that determine an encounter. On the Oracular Power of Dice, how old school gaming relies on creating a story from random rolls. The Classic Dungeon Crawl, a series of posts discussing why the dungeon crawl is a liked playstyle, and its design space. Proceduralism, on what a procedure is and why it is good for a classic game. Classic D&D: I used to think... Why Old D&D may not be as outdated as you think.	Tips on Running FKR: It's Not The Amount of Rules FKR - A Non-Exhaustive Analysis Less Rules to do More Make Adventures not Systems Yes, You Can Resolve Action Without Dice and Do It for Years How I Run and Play an Ultralight Game
On Rules, and House Rules XP for GP: What are the Alternatives?, discussing how to justify XP for GP and alternatives, should you decide it's not appropriate. Necropraxis House Rules, what it says on the tin. Necropraxis Starting Equipment Packs, instead of buying equipment at character creation, roll up a starting pack. Delta's D&D House Rules, what is says on the tin. FISTFUL OF CRYSTALS, a detailed set of house rules for running OD&D in the author's setting. CHAOS REIGNS, an alternative combat procedure for OD&D. KILLCHAIN, a mass combat procedure for OD&D. Ode to 74, full ruleset based on original game.
Dungeons, and their Design Stocking Nightwick Abbey, a stocking procedure used in a real game. The Primordial Stack, a historical look at dungeon delving and its roots. So You Want to Build a Dungeon?, a nearly comprehensive guide of principles and concrete advice for dungeon design.

Gygaxian Style

Arnesonian Style

Game Rules

PDFs of the booklets, I don't recommend actually buying this. Much better options below.
Fantastic Medieval Campaigns, a faithful recreation of the original text.
Delving Deeper, a re-edited (and slightly clarified) retroclone.
Swords and Wizardry Complete, a pretty fleshed-out retroclone with numerous modifications.
White Box: Fantastic Medieval Adventure Game, a streamlined retroclone with numerous pain points and tables condensed into even a single number, sometimes.

Game Rules

Long-form Wisdom

Philotomy's Musings, which discusses the common objections to OD&D, and how to make sense of what the game rules mean.
Muster, which discusses the player expectations and referee guidance on running OD&D (or similar rulesets) as a fantasy wargame (as was intended!).

Musings & Commentary

What We Mean When We Say “Encounter”, understanding how to interpret the rolls that determine an encounter.
On the Oracular Power of Dice, how old school gaming relies on creating a story from random rolls.
The Classic Dungeon Crawl, a series of posts discussing why the dungeon crawl is a liked playstyle, and its design space.
Proceduralism, on what a procedure is and why it is good for a classic game.
Classic D&D: I used to think... Why Old D&D may not be as outdated as you think.

Tips on Running

On Rules, and House Rules

XP for GP: What are the Alternatives?, discussing how to justify XP for GP and alternatives, should you decide it's not appropriate.
Necropraxis House Rules, what it says on the tin.
Necropraxis Starting Equipment Packs, instead of buying equipment at character creation, roll up a starting pack.
Delta's D&D House Rules, what is says on the tin.
FISTFUL OF CRYSTALS, a detailed set of house rules for running OD&D in the author's setting.
CHAOS REIGNS, an alternative combat procedure for OD&D.
KILLCHAIN, a mass combat procedure for OD&D.
Ode to 74, full ruleset based on original game.

Dungeons, and their Design

Stocking Nightwick Abbey, a stocking procedure used in a real game.
The Primordial Stack, a historical look at dungeon delving and its roots.
So You Want to Build a Dungeon?, a nearly comprehensive guide of principles and concrete advice for dungeon design.