Slack - A messaging app for teams who see through the Earth!
LibriVox - free public domain audiobooks
Mattermost - Mattermost is an open source alternative to Slack.
Audible - Audible is the world’s largest provider of premium audiobooks and spoken word content.
Espresso Chat - Productive conversations start here
Mobilism.org - A home for book lovers, app enthusiasts, and much more.