The Tweet Hereafter - The last tweets of the deceased
W3C Markup Validation Service - Validates HTML markup of web pages, one at a time.
Your Life In Weeks - A spreadsheet of your life inspired by Wait But Why
HTML Validator - HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla.
Startup Graveyard - History shouldn't have to repeat itself
Rocket Validator - Site-wide Accessibility and HTML validation made easy. With a single click, Rocket Validator will check thousands of web pages on your site for Accessibility and HTML conformance, producing a detailed, actionable report on seconds.