Telegram
Free
Telegram is a free cloud-based instant messaging platform.
Facebook Messenger
Free
Facebook Messenger is the official Facebook app that lets you have text conversations with all of your friends on the popular social network.
Jitsi
Open Source
Jitsi (formerly SIP Communicator) is a free and open source multiplatform voice (VoIP), videoconferencing and instant messaging application.
IM+
Freemium
IM+ supports simultaneously major IM services, including Google Talk, Twitter DMs, Yahoo!, AIM/iChat, ICQ, Jabber (and Slack through Jabber), etc.
Compare Psi with alternatives
Compare Facebook Messenger and Psi and decide which is most suitable for you.