Gajim - Full featured and easy to use Jabber client
Empathy - Apps/Empathy - GNOME Wiki!
IM+ - Chat everywhere! IM+ is the most widely used mobile IM app! Connect all-in-one to MSN, Yahoo!, Goo...
Tencent QQ - Tencent QQ is a free instant messaging computer program developed by the Chinese company Tencent Holdings Limited.
AirMessage - Use iMessage on any Android phone 💬
Trillian - Trillian is a decentralized and federated instant messaging platform that lets your whole company send private and group messages, keep tabs on what co-workers are doing, share files, and much more.