It may have a silly name, but Weddar takes a new and interesting approach to weather forecasting. Instead of just relying on professional weather forecasting services, it instead uses a crowd sourcing model to provide you with more accurate details on what the weather s currently like in an area that you'll be visiting soon.
When you check the weather in that area, someone has actually filed a report to give an exact description of what conditions are currently like. So, for example, someone in a park nearby may report that the weather is perfect, whereas another person walking a long the river may report that it's hot, but quite windy. Like Foursquare, people get points for adding weather details in a particular location, so the app is sort of like a fun game, too.
It's far from perfect and needs more users to become really worthwhile, but Weddar is an interesting concept nonetheless.