| OBSCURE BATTLES 2 - COLD WAR - A MODULAR BOARDGAME FOR TACTICAL SCALE ENGAGEMENTS IN 1947-1995 PERIOD | Obscure Battles | pdftxt | |
| Ocean | Atarashi Games | pdf | |
| Odious Uplands | Hydra Cooperative | pdf | |
| Odious Uplands Map Pack | Hydra Cooperative | pdf | |
| Offworlders | Chris Wolf | pdf | |
| OGA digital - OGA | Exalted Funeral | pdf | |
| Ominous Crypt of the Blood Moss | Oneiromantic Press | pdfzip | |
| One Page Dungeon Compendium 2013 Edition | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium 2014 Edition | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium 2015 | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium 2018 Tenth Anniversary Edition | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium 2019 Edition | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium: 2010 Edition | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium: 2011 Edition | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium: 2012 Edition | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium: 2016 Edition | Shattered Pike Studio | pdf | |
| One Page Dungeon Compendium: 2017 Edition | Shattered Pike Studio | pdf | |
| One Page Solo Engine | Inflatable Studios | pdftxt | |
| Operation: Nazi Smasher (5E) | Legendary Games | pdf | |
| OPTIONAL RULES GAZETTE v.1 | | pdf | |
| OSR character Sheet | Lazy_Litches_Loot | pdf | |
| OSR Character Sheets Demonic Edition | Random Order Creations | pdfrtf | |
| Ouroboros OSR | Sean Smith | pdftxt | |
| Overland | Frog God Games | zip | |
| The Oceans Are Endless on Meridian | McFin | pdfzip | |
| The Old Lords of Wonder and Ruin | Alchemic Raker | pdftxt | |
| The Oldskull Manifesto | Kent David Kelly | pdf | |
| Øone's Blueprints: The Great City, Cold Crypts | 0one Games | zip | |