jStates is a java library for easy state machine design and implementation.It uses XML to define states and state transitions. jStates is aimed at easy integration with desktop J2SE applications, Struts, Commons Validator, Web and other J2EE technologies
Eclipse plugin based on JTidy, the Java port of HTML Tidy. For (X)HTML and XML files, it provides a Validator (Manual or automatic checking) and a Formatter based on numerous preferences.
Reptile is a web server made in Python. It supports server side scripting with "Embedded Python", PHP, and CGI scripts.
It has an integrated HTML/XMLvalidator that checks the pages before publication and others handy features.