VoiceThread is an online version of the program Photostory. An online tool that is a multimedia slideshow where one can use voice to add comments add audio files or video. Group conversations are collected and shared in one place.
Youtube video that demonstrates what Voicethread is:
http://www.youtube.com/watch?v=yW2nb7FO7p8
There is voicethread for K-12.
VoiceThread: https://voicethread.com/products/k12/