Proloquo 2.0.5 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The actual developer of this software for Mac is AssistiveWare. We recommend checking the downloaded files with any free antivirus. Proloquo for Mac lies within Communication Tools, more precisely Texting & Video calls.
From the developer:
Proloquo is a multilingual speech and communication solution for Mac OS X that provides: a full-fledged communication system (AAC) for people who cannot speak, speech feedback in any application while typing for children and people with learning disabilities. You may also serve as a talking word processor.
You may want to check out more software for Mac, such as LayoutKitchen, which might be similar to Proloquo.