TT5

TT5 is a free conferencing system that allows users to participate in conferences over the internet. Users can communicate via VoIP, stream media files, and share desktop applications such as PowerPoint or Internet Explorer.
The TeamTalk version for Android is designed with a special emphasis on accessibility features for people with visual impairments.
Key features:
Real-time communication via VoIP
Public and private instant messaging
File sharing between group members
Private rooms/channels for each group
High-quality audio codecs (mono and stereo)
Push-to-talk (PTT) and voice activation
User authentication via accounts