MockFlow - A super easy wireframing tool with all the other tools you need in the product design process
Selenium - Selenium automates browsers. That's it! What you do with that power is entirely up to you. Primarily, it is for automating web applications for testing purposes, but is certainly not limited to just that.
Axure - The most powerful way to plan, prototype and hand off to developers, all without code. Download a free trial and see why professionals choose Axure RP 9.
Sauce Labs - Test mobile or web apps instantly across 700+ browser/OS/device platform combinations - without infrastructure setup.
UX-App - HTML5 all-in-one mockup & prototyping tool that exports completed interfaces to working HTML + Javascript
Browsershots - Browsershots makes screenshots of your web design in different browsers.