The froe (also called frow, fromard, frommard, frower, or rending axe) is a tool used for splitting wooden strips from a log. The froe resembles a long thick knife around a foot in length. There is an eye on one end where a (usually) wooden handle is attached. Froes are usually made of iron or steel.

Froes are used to split shingles, kindling, and lath from larger blocks of wood. Curved versions of the froe were also used by coopers to split rough barrel staves. Froes were once a very common woodworking tool until about a century ago when the invention of the power saw made it easier to saw lath and planks from logs. Despite their lack of popularity froes have several advantages over saws. Since they produce no kerf they produce less waste. Planks split with a froe are generally stronger as well since they are split along the grain.

To use a froe the block of wood to be split is set against something solid. The blade of the froe is placed against the end grain of the block and the dull edge of the froe is struck with a wooden mallet or club, driving the froe blade into the wood. Using the handle as a lever the froe blade is twisted, forcing the wood to split. The froe blade is pushed or tapped further down the rift, widening the split until the two halves are separated.

Sloane, Eric. A Museum of Early American Tools. New York: Funk & Wagnal. 1964
Hack, Garrett. Classic Hand Tools. Newton: The Taunton Press. 1999

In case you were curious this site has pictures of a froe, and step by step instructions on how to forge one.

And here is a picture of the curved type froe used in coopering.