A VoixeXML Interpreter, does just what it says - it interprets VoiceXML documents.  But does not, by itself, recognize speech or output speech responses.  It is the core smarts of a VoiceXML platform, but does not have the Application Programming Interfaces ("API") necessary to communicate with an ASR and TTS and/or PBX systems.

A VoiceXML Browser contains a VoiceXML interpreter, and includes generic APIs to ASR, TTS and PBX systems.  However it does not, by itself, recognize speech or output speech responses.  It still requires separate ASR and TTS and/or PBX systems, and its  APIs still need to be modified to work with specific ASR/TTS/PBX systems.

A VoiceXML platform, is a 'turnkey' VoiceXML Speech Recoginition and Text to Speech System that works with a PBX.  It works 'out of the box' and includes a VoiceXML Browser and the required TTS, ASR and PBX subsystems.  A VoiceXML platform may also be called a 'VoiceXML Spoken Dialog System'.