From the intro:
STRANGE TALES OF THE CENTURY (or STotC) is a supplement (and kind of a sequel) to SPIRIT OF THE CENTURY (or SotC). STRANGE TALES will provide your SPIRIT game with lots of new material, including new eras, archetypes, stunts, gadgets, and locations. STRANGE TALES will also provide you with guidelines and suggestions to adapt both SotC and STotC to FATE CORE, the latest evolution of the award-winning FATE roleplaying game system upon which SPIRIT was originally built. Finally, STRANGE TALES acts as a resource to bridge the time between SotC and the upcoming SHADOW OF THE CENTURY RPG from Evil Hat.