wireframes
Here is an article that contains a list of wireframing tools:
http://www.creativebloq.com/wireframes/top-wireframing-tools-11121302
pencil.evolus.vn - open source, cross platform
wireframe.cc - web based subscription
moqups.com - web based subscription
It looks like many of the available webdev wireframe tools for web page layout mockup are web base applications that require paid monthly subscriptions for full access use. These sort of web based applications are becoming more a more prevalent phenomenon as commercial application developers combat "piracy".
