DirtyMarkup combines the power of HTML Tidy, CSS Tidy, JS Beautify, and the Ace editor to effortlessly clean up your messy code.
Pencil is built for the purpose of providing a free and open-source GUI prototyping tool that people can easily install and use to create mockups in popular desktop platforms.
For wireframe-creation. It can also create prototypes by linking different pages of your project. So you can do something like “activate this and that will happen.”