The list of topics in the sidebar is generated using a small plugin of mine, which is an addition to the Tag plugin. This is one thing I like the most about DokuWiki: it is simple and well-documented, so that it is easily extensible!

In my opinion, this should be integrated directly into the tag plugin, which is why I did not plublished it directly to the DokuWiki plugin index. I'll propose that to the tag plugin authors when I'll find the time. Feel free to do so yourself if you want to speed it up. In the mean time, here it is.

The plugin is a syntax plugin used as follows:

{{taglist>tag1 tag2 ...}}

for a list of tag links separated by commas inside a span, and:

{{taglist>tag1 tag2 ... &list}}

for a list of tag links inside a ul list.

It is available here.