From the website:
"A supplement designed for use with any old school rules, allowing you to add new classes, spells, an alternate combat system, and much more!"
"A Curious Volume of Forgotten Lore is not a stand-alone game. It is a rules supplement intended for use with other games such as AD&D, Labryinth Lord, Swords & Wizardry, OSRIC, etc. It contains:
Five new character classes: bard, jester, mystic, savant, mountebank
Hundreds of new spells
A new alternative combat system that is at once streamlined and more realistic
Rules for shipborne adventures and combat
Quick and easy rules for common hazards and weather
New magic items
And much more!"