At it's most basic this macro lists all the tags used in you tiddlywiki as dropdown lists of all the tiddlers which have that tag
For example
<<allTags>>

Displays as:
bag
tiddlywiki-com-ref_public
created
Fri, 11 Feb 2011 14:39:53 GMT
creator
colmbritton
modified
Fri, 11 Feb 2011 14:46:08 GMT
modifier
colmbritton
tags
macro