Caustik wrote a neat program that lets sprites walk around on your desktop and perform all kinds of random interactions with each other. The program is networked as well, so if you throw a sprite off of your screen it actually goes to another user’s desktop.
Sprite Editor is what it sounds like – it is basically an editor to streamline creation of sprite *.spr and *.spi files. Create your own custom sprites then submit them on the sprites forums and all the users will be able to see your creations.
To get started with it, try right clicking the sprite tree to access the many features or read the User Guide by following the link at the top.