"The Media Resource Control Protocol (MRCP) is an Internet Engineering Task Force (IETF) specification that describes a standard interface to media processing resources providing capabilities such as automatic speech recognition (ASR), speech synthesis (text-to-speech or TTS), as well as speaker identification and speaker verification (SI/SV). The key benefit of this technology is that it allows VoiceXML browsers to inter-operate with third party ASR, TTS, and SI/SV servers using an open, standardized protocol. Interoperability of this nature allows a given VoiceXML solution to be comprised of components from multiple vendors, benefiting technology providers by adding value to their products, while placing greater flexibility and choice in the hands of customers."

Two versions are available: 

Acapela MRCP add-on 1.301

This version is a Standard Interface between VoiceXML Platforms and Acapela TTS for Windows Server.
This add-on works only in conjunction with Acapela TTS for Windows Server or Acapela TTS for Linux Server and support the MRCP 1.0 protocol.
Available for Windows Server 2003/2008/2008 R2 and Linux RHEL 3, 4, 5 and 6.x

Acapela MRCP add-on 2.001

This new architecture is based on the award winning UniMRCP open source project.
Acapela MRCP add-on 2.0 is a plugin to the UniMRCP server stack which implements MRCP 2.0 protocol.
Available for Windows Server 2003/2008/2008 R2 and  linux RHEL 4, 5 and 6.x