The leeboard is a very useful invention for recreational and trade-based sailing.  It is a board on a boat that sticks down into the water and acts like an underwater sail.  If used correctly, it allows boats to travel against the wind, so sailors didn't have to wait until the wind favored their direction.  This allowed trade boats to move much more quickly, and so allowed trade to increase.

Date of Invention:
unknown, but during the T'ang dynasty

Inventor: 
Unknown

Importance to Chinese civilization:
Helped bring in money from trade; helped increase trade with other countries, especially those that were relatively far away

Importance to other civilizations:
Increased trade