Jabble is a minimalist XMPP / Jabber instant messaging client, in command-line.
I wrote it some years ago (2006) when I tested a lot of altervatives OS and wanted to chat with my friend.
It is written using only C ANSI functions to be fully portable.
I compiled it successfully on Windows 95/XP, BeOS, AtheOS, FreeBSD, GNU/Hurd, and GNU/Linux 32/64bits. It crashed on QNX.
It does not include SSL/TLS, but you may connect by SSL through "stunnel", a SSL proxy.