Rambox is a Open Source and Cross Platform messaging and emailing application that combines many common web applications into a single interface.
Instead of using multiple apps or having to use your web browser, you can access and manage all your online services from a single application. Rambox currently supports Gmail, Outlook, iCloud Mail, Skype, Steam Chat, TweetDeck, WhatsApp, Slack, Telegram, LinkedIn Messenger, ICQ, Hangouts and many other service providers, even custom services.
More info Rambox for Linux
# Ubuntu tested
~/Downloads$ chmod -x Rambox-0.5.12
~/Downloads$ cd Rambox-0.5.12
Screenshots Rambox for Linux
Rambox add Gmail, Inbox and Outlook support, while Rambox includes Hushmail, mysms, Voxer, Outlook 365 and many others, as well as the ability to add other chat services manually.