Burner - Disposable phone numbers -- now with MMS photo support
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Hushed App - Hushed App will allow you to receive a Secondary Phone Number for Private, Long-Distance...
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.
CoverMe - Private texting, calling, vault
Zulip - Chat for distributed teams. Zulip combines the immediacy of real-time chat with an email threading model. With Zulip, you can catch up on important conversations while ignoring irrelevant ones.