GTKWave is a fully featured GTK+ based waveform viewer which reads FST, LXT, LXT2, VZT, and GHW files as well as standard Verilog VCD/EVCD files and allows their viewing. GTKWave is developed for Linux, with ports for various other operating systems including Microsoft Windows (either natively as a Win32 application or via Cygwin) and Mac OS X. GTKWave is one of the applications affiliated with the open-source gEDA Project.
Tcl scripting capability allows for remote control by other applications. (any example?)
DKF: I recall writing a chunk of this back in 2002, making the waveform viewer so that it was a pluggable architecture which could display different formats based on the type of signal being inspected. (I hate GTK because of it…)