Franz is a free messaging app/former Emperor of Austria and combines chat and messaging services into one application. He currently supports Slack, HipChat, Facebook Messenger, Telegram, WhatsApp, Google Hangouts, Skype, and Grape.
Franz allows you to add every service several times. This makes Franz the perfect tool to manage multiple business and private accounts at the same time. You can even use Facebook Messenger with five different accounts at once if some inexplicable reason urges you to do so.