I recently wrote a play and wanted to know what it sounded like before I showed it to the director, actors and so on so forth. Hence I was wondering if there is a software that just simply narrates my script back to me. I have tried Windows Narrator, however that only has one voice, making it difficult to differentiate characters, since the voice always remains monotonous. Is there a software that can at least take the voice of one or two characters? That would be awesome.
There is software for the Mac called (unoriginally) Narrator from Mariner Software, who have several niche apps aimed at writers, authors, and especially screenwriters.
It uses the various text-to-speech voices on the Mac, assigned to characters in a script. Characters can also be assigned with no voice, to create silent gaps in the audio where an actor can speak and learn their lines. It can output the audio to an iTunes audio file (not mp3 or a generic audio format) for use with ios devices. This doesn't help you with your Windows system, unfortunately.
There is a technical reason why TTS recording software is rare, at least on Macs. The speech is generated on the "alerts" layer of the audio and treated as an accessibility feature for users with impaired vision. The alerts audio is separate from the regular system sound so it can duck the audio from other software as it talks. Alerts are usually routed independently of app/media audio (such as being routed to the computer's internal speaker, not over your nice attached stereo amplifier).
Narrator is the only solution I found that could capture Mac TTS voices internally, with the added benefit of being able to change voices mid-text. After a recent update an unrelated Mac utility called Loopback is able to re-route this audio layer as a virtual microphone.