Place your fruit of choice in a blender or food processor and purée.

If the fruit you choose has seeds (strawberries, watermelon) or is particularly fibrous (mango), strain through a fine mesh strainer.

Pour into a 9x13 baking dish and place in the freezer. Stir every 30 minutes or so to break up any clumps. After about 2 hours remove from freezer; you should have a nice, slushy mix. If it does harden, try scraping with a spoon.

Experiment with adding flavors; basil complements watermelon, mint works with lots of fruits, cayenne pepper will add unexpected heat. Try adding a little vanilla to your simple syrup for a hint of warm flavor.