xkbprint
The X.Org utility that draws the current keyboard as PostScript, with each key's symbols printed in the right place.
XKB describes not just what the keys mean but what the keyboard looks like: rows, key sizes, where Enter sits and what shape it is. Almost nothing ever uses that geometry, with one exception. xkbprint :0 reads the description from the server and writes a PostScript or EPS file picturing the keyboard, each key labelled with the symbols it produces on every level.
It is the quickest way to see what a home-made layout actually does, or to get a sheet of paper to tape next to the monitor while learning Dvorak or a layout for a language you don't type every day. The tool shipped with XKB in X11R6 and has changed about as little since as the geometry section it reads.