has anyone developed a command that calls up a unicode table? that is, similar to Mac OS's Character Palette or Windows's charmap.exe?

The purpose being that user can visually lookup unicode glyphs by category, and pick out the one she wants. This categorization can either be unicode defined subranges (charmap has done), or more arbitrarily defined categories that groups symbols commonly used by particular field (e.g. math, arrows, printer's symbols, phonetics, letter like, musical... (as done by Mac OS X)).