Dragonsteel

Dragonsteel is an unpublished series set on Yolen that has been revealed to be the prequel of the Cosmere. In terms of chronological events, this series will take place before any other series and will feature the Shattering, Hoid's backstory, and dragons. The chief reason that Sanderson hasn't prioritized this series over others is that he doesn't want readers to feel that there is a prerequisite amount of knowledge needed to read his other books and understand what's happening. He also probably won't publish it until Hoid's story becomes relevant. His plan is to rewrite and publish Dragonsteel sometime after both arcs of the Stormlight Archive has been completed.

About
"Dragonsteel is an unpublished series set on the Shardworld Yolen. The first two books form a duology, with Hoid as a major character. They are preliminarily titled "The Liar of Partinel" and "The Lightweaver of Rens". The first one, and perhaps the second one as well are set before the Shattering of Adonalsium. Brandon will not show anyone these books, and I don't think he's even written them both. There are five more books that occur hundreds of years later, so not "directly" a series, but still the same world. These five are the core Dragonsteel sequence, the first of which Brandon wrote for his master's thesis at BYU. It is still in the library there. Many things have changed since then, so this book is no longer canon."

- User: Windrunner on Dragonsteel and related stories