Cross Browser Tools

Ghostlab - Synchronized browser testing for web and mobile. Test files and URLs against multiple devices by syncing clicks, scrolls, keystrokes across the devices. $49 for a license.
Edge Inspect CC - Synchronized Browsing & Refreshing. Test files and URLs agaisnt multiple devices at once. Part of the Adobe Creative Cloud.
Live Reload - LiveReload monitors changes in the file system. As soon as you save a file, it is preprocessed as needed, and the browser is refreshed. $10 for Mac. Free for other platforms.
Parallels - Run Windows on Your Mac. Useful for testing Internet Explorer on OSX.

Google Chrome Tools

UX Check - UX Check is a Chrome Extension that helps you identify usability issues through a heuristic evaluation. It gives you tools for making notes on websites.
Good UI - Data stories concerning UI. Tips and hints for a better user experience. They have a paid-for newsletter.
Little Big Details contains design inspiration from the point of view of the users.
Adobe Color CC - Formerly known as Kuler, this tools lets you pick color schemes.
Material Palette - Preview simple color schemes. Pick two colors and preview what they will look like on a simple site.

W3Techs has a lot of technology surveys that can show you current technology trends. It will show changes in market share, which CMS systems are popular, etc.
Stack Share - see what technology stacks other platforms are using.