Franz is a free messaging app / former Emperor of Austria and combines chat & messaging services into one application. Franz currently supports Slack, WhatsApp, WeChat, HipChat, Facebook Messenger, Telegram, Google Hangouts, GroupMe, Skype and many more. You can download Franz for Mac, Windows & Linux.
Franz allows you to add each service many times. This makes Franz the perfect tool to manage multiple business and private accounts all at the same time. You could even use five different Facebook Messenger accounts at once, if some inexplicable reason urges you to do so.