OG Blueprints will never be _directly_ ported to D6 - when the time is right, it will be rewritten as a core part of CTools/Panels.
Organic Groups Blueprints is a system for creating and managing 'bundles' of 'blueprints' that are attached as OG panels to organic groups. The module is constructed on Panels2 and Organic Groups, and Organic Groups Panels (which is part of the normal OG package). Even if you're already familiar with those modules, OG Blueprints uses some new jargon that you'll need to learn. Because blueprints & bundles are a pretty abstract idea, I've included both technical and metaphorical explanations:
Technical Overview
See README.txt for the technical overview.
Silly Metaphor
Panels & Displays: Not new, but important. Displays can be thought of as page layouts that are composed of rows/columns/regions, each of which is itself a 'Panel'. Each Panel holds a number of Panes; panes can be edited and filled with all sorts of content via the Panels GUI.
The Taxonomy VTN module provides an index for vocabularies, terms and nodes just like those you find at the end of reference or technical books. It supports synonyms, terms, related terms, and parent/child relations. The root Taxonomy VTN path is http://www.example.com/taxonomy_vtn
On June 15, 2009 I fixed a couple of problems: the master index would show the first description found for all the entries. The Node back link when coming from a parent/child page would send you back to the main vocabulary page with all the terms.
Block Class allows users to add classes to any block through the block's configuration interface. By adding a very short snippet of PHP to a theme's block.tpl.php file, classes can be added to the parent <div class="block ..."> element of a block. Hooray for more powerful block theming!