ShadowDark

ShadowDark is a modern OSR by The Arcane Library that takes the bones of old-school dungeon crawling and updates it with newer design sensibilities.

The most notable feature of the system is that torches lit in game last 1 hour of real world time, encouraging players to keep moving and waste little time. This can be a great mechanic for groups that have limited play time for each session.

The Arcane Library offers a free quickstart that comes with a digital copy of the players guide and the game master guide. It has pregenerated characters, but also all the rules needed to create your own custom adventurers. It also comes with a sample dungeon crawl, Lost Citadel of the Scarlet Minotaur.

They also offer a free dungeon generator that has lots of tables to create new dungeons once the first once is conquered.

If you need characters quick, and don’t want to use the pregens you can also use their free character generator: ShadowDarklings.