Simple, all-in-one test to check the quality of your website
Passmarked is THE tool I've been looking for to check the quality of websites (mine & clients'). The open source list of tests makes it incredibly useful and flexible for integrating into the development workflow. It's only just been launched but there's already a tremendous amount of coverage that will only get better as more people contribute.
AccessLint brings automated web accessibility testing into your development workflow. When a pull request is opened, AccessLint reviews the changes and comments with any new accessibility issues, giving you quick, timely, and targeted feedback, before code goes live.