BikeCAD is a free online bicycle design tool. BikeCAD requires Java which can be downloaded from: www.java.com. The video above demonstrates how icons in BikeCAD open dialog boxes that allow you to change all aspects of a bike's geometry.
It's worth having a free account on the BikeCAD.ca web site. Having one allows you to save designs to your My Designs section which is only visible to you. You can also contribute your designs to the public Design Archive and participate on the BikeCAD forum.