ProSynth 2.1 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. The software lies within Education Tools, more precisely Languages.
This free program was originally designed by Mark Huckvale, University College London. The following version: 2.1 is the most frequently downloaded one by the program users. Prosynth2.exe is the most frequent filename for this program's installer. We recommend checking the downloaded files with any free antivirus.
From the developer:
The ProSynth Windows application can be used to demonstrate all-prosodic speech synthesis - synthesis from a combination of a rich hierarchical phonological structure with declarative knowledge for phonetic interpretation. With ProSynth you can see text being converted to phonological form and then to sound stage by stage. You can even customise ProSynth for your own research in speech synthesis
You may want to check out more software, such as cdrLabel Dutch Nederlands Language DLL, I Can Read the Prayers in Hebrew or Babylon-Pro, which might be related to ProSynth.