HTML / PHP / CMS
Statuscodes
https://de.wikipedia.org/wiki/HTTP-Statuscode
Links
https://subgraph.com/vega/download/index.en.html - Vega Vulnerability Scanner
http://popuri.us/ - PageRank / link popularity check
http://validator.w3.org/ - W3C Markup Validation Service
Bluefish - HTML / PHP editor for Linux, supports direct edit on FTP
http://ckeditor.com/demo - Online WYSIWYG Editor
SELFHTML - HTML / PHP reference