MockupScreens is a tool to extremely quickly create screen mockups that don't look like real screens. You organize mockups into scenarios.
As it states on the website (http://www.mockupscreens.com/):
MockupScreens' purpose is rapid screen prototyping. So what does it do? With MockupScreens you quickly and easily create screen mockups of your application, while the coding hasn't even started yet. MockupScreens main design goals are ease of use and productivity.
Actually, I was doing screen mockups on many projects and I was quite unhappy with tools support. How to effectively maintain, comunicate or e-mail paper sketches? How to populate rows in datagrid in some GUI tool? How to organize mockups? Only tool that made me moderately satisfied was QtDesigner, but I knew there should be a better way. I just didn't want to waste hours just to sketch the screens of a scenario - I wanted to focus on the problem I was trying to solve, not on some tool or the process.
Finaly, I got fed up with inaction, and wrote a small tool to help me. It was started as a PetProject?, but it has grown since into quite a helpfull little tool. If you are curious, check the website: http://mockupscreens.com :-)
To be unbiased, see the GuiPrototypingTools
See also: DeadlyGuiPrototypesCategorySoftwareTool