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What website wireframing tools are available online, or self-hosted?

I've got a very large web poject ( site) and i'm searching for good mockup application that helped me to design and architect the website.

Any suggestions?

Balsamiq can be used by plenty of places and is regarded as simple to use.

Take a look answer and also the question http://ux.stackexchange.com/questions/14365/how-to-create-mockups-of-user-interfaces/14368#14368

You'll find there several choices