1. Combine cranberries, sugar, ginger, and 2 cups water in a medium saucepan. Cover, and bring to a simmer; cook, stirring occasionally, until berries have burst and softened, about 10 minutes. Pass through a sieve into a medium bowl, pressing on solids with a wooden spoon to extract as much liquid as possible; discard solids.

2. Meanwhile, sprinkle gelatin over 1/2 cup water in a bowl. Let soften 5 minutes. Add cranberry mixture; stir until gelatin has dissolved. Refrigerate, in an airtight container, at least 4 hours (or up to 1 week).