I've written my own, mostly using the linux-gpib Perl library. I've also written a perl wrapper for my instruments so I can do queries from the shell:
$ pspq *idn?
HEWLETT-PACKARD,E3631A,0,2.1-5.0-1.0
$ dmmq # read value from 3478A
+0.47033E+0
Or, set things:
$ psp "APPL P6V, 3.3, 0.1" # set 6V output to 3.3V@100mA
$ psp "OUTPUT ON"
With this simple interface, most everything I need gets written in bash. Occasionally, I've written some projects directly in Perl or C if I needed faster acquisition or control.
After getting the data, I usually use gnuplot for simple plotting, or octave for any signal analysis.
I've been pretty happy with the "roll your own" approach. There's certainly no support for linux-gpib, or Linux in general, from any equipment manufacturer that I'm aware of.