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[Steve Cassidy]:  "[Trf] lets you zip up a bit of data but doesn't provide the machinery to zip
directories or files.  mkZipLib [http://mkextensions.sourceforge.net/]
provides such an interface as does zvfs
[http://www.hwaci.com/sw/tobe/zvfs.html].  More up to date is the zipvfs
package which is part of [tclvfs] but that doesn't seem to be working cleanly
yet and requires tcl8.4 features."

http://www.equi4.com/critlib/zipper.README
http://www.equi4.com/critlib/zlib.README

See also [Using a zip file as a Tcl Module].

See also [Using zipper to create zip files].

Also, explain pkware vs. winzip vs. zLibDll.

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[NEM] zip is also the name of another [functional programming] classic. You can think of it as a
function that takes a bunch of "columns" (think relational) and returns a list of "rows":

 proc zip {cola colb} {
   set ret [list]
   foreach a $cola b $colb { lappend ret [list $a $b] }
   return $ret
 }
 zip {1 2 3} {a b c} ;# returns {{1 a} {2 b} {3 c}}

You can generalise zip to zipWith which applies an arbitrary function on each pair of values from
the columns:
 proc apply {func args} { uplevel #0 $func $args }
 proc zipWith {f cola colb} {
   set ret [list]
   foreach a $cola b $colb { lappend ret [apply $f $a $b] }
   return $ret
 }
 interp alias {} zip {} zipWith list

You could further generalise the function to take an arbitrary number of columns. I'll leave that,
and the reverse unzip operation as exercises. See also [fold], [filter], [iterators] and [map].

''[Lars H]: Isn't that more commonly known as "transposing"? See [Transposing a matrix].''

[NEM]: Depends who you ask. zipWith is more general, though.
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[Category Compression]