Spade makes it easier to manage your farm at the Sunsong Ranch:

Right-clicking on a Tilled Soil patch will display an OPie ring (requires OPie; install separately) containing all your seeds, making planting things a breeze. ALT-Right-clicking will display a ring containing all your seed bags.
Right-clicking on Parched or Infested crops will automatically use the watering can or bug sprayer if you have those in your bags.
ALT-Right-clicking on Growing crops will remove them from your farm if you carry a shovel in your bags.
ALT-Right-clicking on Untilled Soil will use the Master Plow, if it is present in your bags, to till the entire row.
Type /spade to view a list of plants growing on your characters' farms. When you log in, Spade will tell if there are plants ready for harvest.

You can change some of Spade's behaviour, or clear the current character's farm, by clicking the cogwheel icon in the title bar of the /spade window.

Official site

Please check the official site for most recent releases. You can also report errors or help translate Spade.