From the PDF:
What is this game about?
It’s about exploring the ruins of the dying world of Zarth. Fighting off the Others, alien monstrosities from outside of your reality. Making your mark on the world before it dives into the sun Nemesis.
What is the Swords and Wizardry system?
It is a retroclone of the original edition of the world’s favourite role playing game system. The rules are simple and streamlined which keeps rulings and dice rolls down to a minimum and encourages imaginative play on both sides of the Crypt Keeper’s screen.
Crypts & Things uses the Swords and Wizardry system modified to better suit the Swords and Sorcery genre. When ever the rule system is referred to it is as Swords & Wizardry. Specifically the game uses the Swords & Wizardry Core (2nd Printing) that is available in Word doc format from the Swords & Wizardry web site.