This plotting package for X-11 was written by David Harrison, between 1986 and 1989. Despite its age, I find it very useful, and I know of no good substitute. I'm distributing it here (as allowed by the copyright notice) because it's not easily available elsewhere.
The xgraph program is particularly useful with my software for flexible Bayesian modeling, since it allows plots produced by that software to be very conveniently viewed by just piping them into xgraph.
The version here incorporates some improvements by Peter D. Gilbert and myself. It was packaged and released on 2000-09-10.
The xgraph program is available in source form (in C), and has been tested on SGI/IRIX, SUN/Solaris, and Intel/Linux systems:
Compressed tar archive (154K)