Some people may ask why not just use Mac OS's native Services and Voiceover? With Natural Reader 16 you have on-the-fly control over voice selection, speech speed, plus you still retrain playback controls, and it shows the text like 'captions' in a tiny but very functional window.
it is basically the webapp but wrapped in an app container, the one exception is that the desktop app includes what was formerly known as the Floating Bar, which is now called the Miniboard and resides under the overflow menu 'More', a feature I use a lot to readback whatever text I've selected with my cursor in whatever app avoiding the need to cut and paste or download and upload. With Natural Reader 16, the desktop app is finally on par with the webapp.
Adamlogan's Experience This is my preferred software solution on Mac OS for text to speech.