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.
SafiServer is an engine that powers the applications called Saflets that control one or more Asterisk PBXs. These can be used for IVR applications such as information, account management, nearest dealer routing, and more. It also acts as an application repository for multi-developer environments.