Wireframing & Prototyping Resources
OmniGraffle – Really good for making very simple wires and screen flows. 14 day trial. Ability to export JPGs and PDFs to use in prototyping resources.
Marvel – Drag and drop JPGs and make hot spots and transitions between pages. Free version available. Best for web prototypes.
InVision – First project free!
POP – Prototyping on Paper. You can use hand sketches, take pictures with your phone, and make hot spots. Best for mobile prototypes.
Keynote – Surprisingly, keynote has the ability to do some really interesting prototype simulations. See this video below as an example!