VoiceThread is an excellent tool for student reflections. Students can choose to create a video, audio, or text-based comment to address an instructor's prompt. It has been my experience that most students will try the audio but prefer text, maybe because they do not like the sound of their voice. Some professors use it instead of asynchronous discussion forums, but I don't think this is a good use as it is difficult to respond to another student's post because the comments aren't organized by threads.
Works on Macs, PCs and iOS devices. Microphones and webcams are recommended but not required.