If you use Facebook Messenger for business chats, think again. Facebook recently admitted it was storing chat conversations for the purpose of "better focusing" their users' "ad experiences". Well, nothing new there - except that if they're storing the data, it's vulnerable to hacks and search warrants.
Cryptocat is another open source solution that ensures a secure chat from within Chrome, Firefox, Safari, and OS X. Using Cryptocat, you can host group conversations, transfer files, and connect with Facebook Messenger.