Pinegrow Web Editor
Pinegrow is a Mac, Windows and Linux web editor that lets you build responsive websites faster with live multi-page editing, CSS & SASS styling, CSS Grid editor and smart components for Bootstrap, Foundation and WordPress.
IETester
A "free browser that allows you to have the rendering and javascript engines of IE8 beta 1, IE7, IE6, and IE5.5 on Vista and XP, as well as the installed IE in the same process."
Paparazzi!
Free Mac software for taking webpage screenshots. Can capture the entire length of a page (beyond the "fold").
urlgreyhot: OmniGraffle Wireframe Palette
An excellent resource for wireframing.