I'm afraid this is the first I've heard of a "txt" flavoured Blosxom. Try dropping the "/+txt" bit from the end of the URL.
I saw that font size feature quite often during the last weeks and I liked it. I first tried to figure out, which system offers that feature and found that at least Serendipity’s freetag plugin offers it, but didn’t want to download Serendipity just for the plugin. So I decided, the algorithm for calculating the font sizes shouldn’t be that hard to find and coded it from scratch by my own. :-)
And while coding it I noticed that changing the color instead of the font size could be done the same way and that this feature isn’t much more difficult. So I implemented it, too.
Another new feature is that you now can configure the minimum number of postings a tag should have to show up in the list of tags.
Now playing: Falco — Der Kommissar