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.
Socialkeeper - Cultivate your friendships
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
FaceCat - Chat anonymously with your friends
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.
Bond - A simple app that reminds you to keep in touch with people