Web Experience Toolkit (WET): Open source code library for building innovative websites that are accessible, usable, interoperable, mobile-friendly and multilingual. This collaborative open source project is led by the Government of Canada.
The WPSS Validation Tool provides web developers and quality assurance testers the ability to perform a number of web site and web page validation tasks at one time. The tool crawls a site to find all of the documents then analyses each document with a number of validation tools. See the link for online documentation and test cases.