Gajim

Privacy Pros: Open source, allows OMEMO and OpenPGP encryption with XMPP clients. Integrates with JMP.chat to communicate via SMS.

Privacy Cons: SMS is unencrypted on receiver’s end. Encryption is not enabled by default.

Privacy Tips: Turn on OMEMO or OPGP encryption via settings. Be aware of SMS being unencrypted.

Fully-featured XMPP chat client

Gajim aims to be an easy to use and fully-featured XMPP client. Just chat with your friends or family, easily share pictures and thoughts or discuss the news with your groups.

Chat securely with End-to-End encryption via OMEMO or OpenPGP.

Gajim integrates well with your other devices: simply continue conversations on your mobile device.

Features:

Never miss a message, keep all your chat clients synchronized
Invite friends to group chats or join one
Easily send pictures, videos or other files to friends and groups
Chat securely with End-to-End encryption via OMEMO or OpenPGP
Use your favorite emoticons, set your own profile picture
Keep and manage all your chat history
Organize your chats with workspaces
Automatic spell-checking for your messages
Connect to other Messengers via Transports (Facebook, IRC, ...)
Lookup things on Wikipedia, dictionaries or other search engines directly from the chat window
Set your activity or tune to show your friends how you are feeling
Support for multiple accounts
XML console to see what's happening on the protocol layer
Support for service discovery including nodes and search for users
Even more features via plugins