Invisible Sun RPG: Book M
Even its name is a secret. Some say it comes from the Sodality of Vryn, which identifies thirteen currents of magic and gives each a letter designation—M is the 13th and most powerful. Others say the title refers to the original writer of the book, while still others believe it stands for mystery, or—perhaps most simply and obviously—magic. This 120-page hardcover comes with 200 spell, ephemera, and object of power cards, plus a beautiful and handy slipcase with room for the next three supplements.
[From the Kickstarter description]