tawk.to - tawk.to is a free live chat app that lets you monitor and chat with visitors on your website or from a free customizable page
Walkaround - Walkaround is a variant of Wave, based on the Apache Wave code base, that runs on App Engine.
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Slack - A messaging app for teams who see through the Earth!
LiveChat - LiveChat - premium live chat software. Approach customers directly on the website, make connections and drive more sales using LiveChat.
Rizzoma - Email and IM are linear contextless communication tools.