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What is the best text-to-speech software for Windows?
What is the best text-to-speech software for Android?
What is the best text-to-speech software for Mac?
I would have to suggest Dragon Naturally Speaking. I have used it myself, and it is pretty impressive. For your purposes, it has a great text-to-speech feature that can be used to convert simple text to quality voice. For the reverse, (speech-to-text) it behaves better as you use the software, as it implements heuristic learning algorithms to better understand how you speak. I also like that it has many other commands, so you can essentially be keyboard free once you learn some of the basic ones You can even browse the web and send emails with it.
For developers, there is also a SDK available, so that you can integrate Dragon into your applications.
I've used MaryTTS which is opensource and I've found to be quite good.
The engine part of it is written in Java and operates as an HTTP service which you can then query from practically any language. It is quite flexible and can be queried in a number of ways with a simple sentence or with extra markup for direct access to phonemic elements or to if you want to specify extra information such as prosody. It delivers several different types of data including xml representations of the transcribed output including as a PCM wave file, which can then be rendered with the audio software of your choosing.