Okay, I know that a book is not technically a tool. But this one may be an exception. The Real Wood Bible by Nick Gibbs is an easy-to-use reference book aimed straight at woodworkers. Using full color photography, this book addresses how to identify 100 species of common and exotic wood, but it goes much further than that. It also identifies their woodworking characteristics, where they come from and their sustainability regarding harvest. It also has a handy glossary: Ever wonder about terms like burl, harewood, oysters and waney?
With advice on subjects from buying wood to radial and tangential shrinkage, this book is useful for woodworkers from beginners to experts. While certainly not exhaustive, Nick Gibbs packs a lot of information into the 256 pages of this missive.
So while this book may not be a “tool” per se, it will likely be of significant value when you actually have a tool in hand.
Published by Firefly Books (ISBN 1-55407-033-3) it is available for around $30 from a variety of sources, including Rockler.com.