phpivr is an Asterisk AGI application which uses PHPAGI to organize Interactive Voice Responses. It doesn't need extensions.conf changes and dialplan reloading if you want to modify the IVR menu, it reads phpivr.conf on the fly. It supports unlimited levels of IVR menus. It is a standalone tool (you do not need to install FreePBX with all its functionality), does not require additional exotic libraries, and is easy to integrate into your own application.
Speech synthesis for asterisk is an Asterisk AGI script that uses Google Translate to convert text to speech and play it back to the user. It supports a variety of different languages, local caching of voice data, and a choice between 8 kHz or 16 kHz sample rates to provide the best possible sound quality along with the use of wideband codecs.