Feature Rich Interactive Prototyping Tool: Lumzy
Lumzy is a free online quick mockup creation and rapid prototyping tool for software designers and developers with robust features, intuitive and clean interface.
You can add events to controls, place controls inside other containers and emulate your project with easy page navigation triggered by user actions.
Add participants to your project and chat within same window over the project. With project participants, you can edit a project online in realtime. When you drag a control, everyone connected sees the changes you just made.