Vacuum IM - it is a free cross-platform Jabber-client 
written in Qt4. The fundamental difference from other 
cross-platform client is open, modular architecture,
which allows the user to customize the functionality
to meet specific needs, as well as use of the existing
modules to develop your own.

Requirements (all already in Slackware):
Qt >= 4.7.0
enchant >= 1.5
hunspell >= 1.3.2
libidn >= 1.24
zlib >= 1.2.5
libzip >= 0.9.3