Arno Welzel

This widget displays top level categories in multiple columns.
After installation, just add the widget to desired sidebar or footer and optionally enter a custom title and the number of columns to be displayed.
By default two columns are used, but you can set any number of columns you like in the backend.
Also see details at <a href="http://arnowelzel.de/wp/en/projects/wordpress/multicolumn-category-widget" rel="nofollow ugc">http://arnowelzel.de/wp/en/projects/wordpress/multicolumn-category-widget</a>.

Multicolumn Category Widget

This widget displays top level categories in multiple columns.

Gary Jones

Can add multiple calendar widgets – each of them set to different categories (or All Categories).
The tooltip on the per-day links shows only post titles from that category, and when you click on the calendar link to bring up the day archive of posts, only posts from that category are shown.

Calendar Category

Un-registers the default Calendar widget, and registers a new one which supports showing only those posts in certain (or all) categories.

Multicolumn Category Widget vs Calendar Category