What are some alternatives?
Trillian - Trillian is a decentralized and federated instant messaging platform that lets your whole company send private and group messages, keep tabs on what co-workers are doing, share files, and much more.
Franz - Franz is your messaging app for WhatsApp, Facebook Messenger, Slack, Gmail, Telegram and many many more.
Jitsi - Open-source video calling and chat platform.
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Station - Station unifies all your work tools in one neat & productive interface.
Facebook Messenger - Facebook Messenger is a faster way to message.