There are a plethora of excellent web design tools available these days, designed to assist you with mockups, frameworks, testing, and other tasks. You'll also find a plethora of downloads on the various elements that comprise good web design, such as but not limited to VR, animation, colours, and typography.
Whatever problem you're trying to solve in your web design workflow, there's a tool for it, whether it's a standalone utility or a feature within a larger app. The even better news is that so many of these great tools are free, though this does make the selection of tools available far more daunting.