JAVIER is a JAvascript Voicexml InterpretER, designed (but not restricted) to run inside a web browser, its main engine has less than 1000 lines of code. It's maybe, the tiniest but (almost) FULL VoiceXML implementation.
VxmlSurfer is a modular, multi-platform, extensible VoiceXML 2.0 interpreter, geared to Web browsing as opposed to telephony. VxmlSurfer is currently used as a user interface for the HearSay non-visual Web browser.