minipageThe minipage environment requires you to specify the
width of the "page" you're going to create. This is sometimes
inconvenient: you would like to occupy less space, if possible, but
minipage sets a box that is exactly the width you
specified.
The pbox package defines a \pbox whose width is exactly
that of the longest enclosed line, subject to a maximum width that you
give it. So while \parbox{2cm}{Hello\\world!} produces a
box of width exactly 2cm,
\pbox{2cm}{Hello\\world!} produces one whose width is
1.79cm (if one's using the default cmr font for the
text, at least). The package also provides a
\settominwidth[min]{length}{text} (which looks (almost)
like the standard \settowidth command), and a \widthofpbox
function analagous to the \widthof command for use with the
calc package.
The eqparbox package extends pbox's idea, by allowing you to set a series of boxes, all with the same (minimised) width. (Note that it doesn't accept a limiting maximum width parameter.) The package documentation shows the following example drawn from a joke curriculum vitae:
\noindent%
\eqparbox{place}{\textbf{Widgets, Inc.}} \hfill
\eqparbox{title}{\textbf{Senior Widget Designer}} \hfill
\eqparbox{dates}{\textbf{1/95--present}}
...
\noindent%
\eqparbox{place}{\textbf{Thingamabobs, Ltd.}} \hfill
\eqparbox{title}{\textbf{Lead Engineer}} \hfill
\eqparbox{dates}{\textbf{9/92--12/94}}
The code makes the three items on each of the heading lines have
exactly the same width, so that the lines as a whole produce a regular
pattern down the page. A command \eqboxwidth allows you to use
the measured width of a group: the documentation shows how the command
may be used to produce sensible-looking columns that mix c-,
r- or l-rows, with the equivalent of a p{...}
entry, by making the fixed-width rows an eqparbox group, and
making the last from a \parbox using the width that's been
measured for the group.
The varwidth package defines a varwidth
environment which sets the content of the box to match a "narrower
natural width" if it finds one. (You give it the same parameters as
you would give minipage: in effect, it is a 'drop-in'
replacement.) Varwidth provides its own ragged text command:
\narrowragged, which aims to make narrower lines and to put more
text in the last line of the paragraph (thus producing lines with more
nearly equal lengths than typically happens with \raggedright
itself).
The documentation (in the package file) lists various restrictions and things still to be done, but the package is already proving useful for a variety of jobs.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=varwidth