Stars Without Number is a great accomplishment. Not just for an OSR, but for any RPG.

3 classes (Warrior, Psychic, Expert) supplemented by training and background packages (1 of each) to produce varied characters.

A strong selection of scifi gear and ships. With solid subsystems for customizing your own starship.

The mechanics are a bit clunky by modern standards but smooth by OSR standards. Very playable.

The setting is intriguing but minimal. A galaxy emerging from a dark age. A second chance to create a human Imperium among the stars.

Sector, Planet, Faction, Adventure, and Alien creation subsystems. A wonderful toolbox to build almost anything a GM might need.

A small bestiary and example sector.

A really excellent 'How to GM' section focusing on Sandbox Style play.

Black and white art throughout, very high quality. The PDF is bookmarked.