a2ps is an Any to PostScript filter. a2ps started as a Text to PostScript converter, with pretty printing features and all the expected features from this kind of programs.
But today, it is also able to deal with other file types (PostScript, Texinfo, compressed, whatever...) provided you have the necessary tools.
Some samples of its Text to PostScript feature are available: in plain style, or in the gray style (and its alternative gray2), or with colors. (Remember! Sometimes you can't trust too much ghostview: print it, then evaluate!)