OK, I got it. The tags written under the tiddler (and enclosed in double brackets if necessary) generate a del.icio.us-type tag map. When you hover over a tag in the tag map, a popup menu appears that lists the tiddlers assigned that tag.

The tags are also accesible via the size-customizable menu on the right-hand side.

The calendar is not automatically generated from what I could tell. It's simply coded and edited by hand.

I guess nobody has coded self-generated calendar tiddlers yet. It would be cool to have calendar-tags which could automatically populate a calendar tiddler.

All this is portable on a USB stick. Heh.