Apache Xalan
Conversion RTF to HTML documents is being carried out with the help of Apache Xalan Project.
The Apache Xalan Project is a collaborative software development project dedicated to providing robust, full-featured, commercial-quality, and freely available XSLT support on a wide variety of platforms. There are currently two subprojects under the Apache Xalan Project: Xalan C++, and Xalan Java, representing C++ and Java implementations of the W3C XSL Transformations (XSLT) Version 1.0 and the XML Path Language (XPath) Version 1.0 recommendations.
Xalan has moved out of the XML project and is now a project in its own right.
Read about Features Converter Software, RTF to HTML feature.