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.
21 Alternatives To Trillian
Bitrix24
Bitrix24 is a free (for small businesses) social enterprise platform. It is a united work space which handles the many aspects of daily operations and tasks. Create your own social intranet in minutes!
Brosix
Brosix will improve the efficiency and decrease the expenses of your business by providing you all-in-one features package and many control functions.
WhatsApp
WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.