Cryptocat - Encrypted open source messenger. Supports file sharing and multiple devices. Available for Windows, Linux and Mac.
Kontalk - A community-driven instant messaging network. Supports end-to-end encryption. Both client-to-server and server-to-server channels are fully encrypted.
Conversations - An open source Jabber/XMPP client for Android 4.0+ smart phones. Supports end-to-end encryption with either OTR or openPGP.