Text to speech for gnulinux?

As I don't need it myself I have no experience whatsoever with using any of these programs but there is a (pretty comprehensive) list online which might be helpful for you: https://en.wikipedia.org/wiki/List_of_screen_readers

First of all, sorry, cause I'm french and i'm gonna give you useful but french links.
The last voice I played with under windows was microsoft sam and I don't know anna.
Under trisquel we have orca preinstalled, but the voice quality is not that good. You can change the ugly voice by connecting orca to a proprietary voice but you'll have to find it by yourself ;) (http://www.framasoft.net/article5118.html). There is also http://www.voxforge.org/ to do this.

You can also check NVDA : http://www.framasoft.net/article4534.html
And http://oralux.org/

You mean a speech sintetizer like

http://espeak.sourceforge.net/

or

http://www.cstr.ed.ac.uk/projects/festival/

?

There are several text-to-speech programs.
https://help.ubuntu.com/community/TextToSpeech

And additional voices:
http://www.firevox.clcworld.net/voices.html

Thank you.

I recognize some of the links stated in the answers. The quality of espeak and festival voices I have installed or tested, is not high enough. I am impressed of the quality of windows voice anna. On the internet there was, and maybe still is, some windows sapi5 voices. Fx english and french voices. Likely not with an legal license. They are all of a high standard. There was at some point an effort to make software, so you could install them on gnulinux. But it stalled. Reverse engineering them to source code, that is usable on gnulinux is not possible?

The cepstral voices I know of. I find the english david voice acceptable. Cepstral mentions the cepstral voices in combination with orca. I downloaded voice david and installed it. And got no error messages. But I could not get orca to use voice david. I did not get voice david to make any sound. I am not that skilled, that I can determine if it can be done on ubuntu 14.04. Cepstral does not provide support. Cepstral linux voices are not free or open source software?

From time to time gnulinux puzzles me. Fx to my knowledge there is no high quality gnulinux video editor. Still pitivi cannot get their crowdfunding funded fast. Maybe there are reasons that a voice of windows voice anna quality is not a priority for gnulinux. I think I once heard, that people who rely on text to speech voices, prefer voices like the orca voices. And often they heavily speed up the voices. If I want to listen to a book converted to an audio book via text to speech, I want the quality level of windows voice anna. If the money came together, getting natural gnulinux voices should be manageable?

I find some of the edinburgh voices acceptable. At some point I wrote edinburgh and asked if I could get or buy their voices. They replied, that they were using underlaying licenses limiting them from turning over the software to anyone. I do not recall asking them who would benefit from their research?

Ivona make acceptable voices. They make many languages. The software is not freeware, nor open source. They only make windows versions. My knowledge is, that they use one basic software technology. I guess algorithms is what it is about. To make a voice, they record human beeings speaking thousand and thousand of words and sentences. They output of the computation of the sound files is voice software.