GoodUI Evidence - People's A/B test results that show which UI ideas work best
BrokenLinkCheck - Free Broken Link Checker / Online Dead Link Checking Tool - find bad hyperlinks
Decidr - Make better decisions with quick A/B polls
Dead Link Checker - Check for broken links on any website
PreFlight - Preflight is an Automated Web Testing tool. Allows everyone to automate Web UI tests.
LinkChecker - LinkChecker is a free, GPL licensed website validator.