STORM is a free and open source tool for testing web services.
It is written mostly in F#.
STORM allows you to
1. Test web services written using any technology (.NET , Java, etc.)
2. Dynamically invoke web service methods even those that have input parameters of complex data types
3. Save development time and money. Creating throw-away test client apps just to test the web service is just too wasteful
4. Test multiple web services from within one UI.
5. Edit/Manipulate the raw soap requests.
6 Others (Try out the tool and find out yourself!)