A nice article by Creative Bloq on the best wireframing tools out there.

On the Freebee list:

Penultimate, Pencil, Mockflow, Framebox, Hot glue

And don’t forget… pen and paper

Wireframing tools
There’s nothing quicker than grabbing a pen and paper
Yes. An actual pen. And some real made-from-wood paper. Okay, so these don’t allow you to make a prototype, and there’s no built-in elements. But, if you feel more comfortable using a more traditional approach, why not get your ideas down on paper first and refine them in software later?
TOPICS

ADOBE
WIREFRAMES
APPS
WEB DESIGN
RELATED ARTICLES

20 top new tools for freelancers
20 brilliant WordPress tutorials
How the BBC found a new way to nurture innovative ideas
10 design resources to save you time and energy