Originally Posted by kovidgoyal
calibre does have a plugin architecture. For a new input format you need to write a plugin to convert format -> html for a new output format you need to write opf -> format. Once you do that, integrating it into calibre is trivial.
Well not really, calibre has a modular design which makes it easy to add features. However this requires the 3rd party tool to get released with calibre. A plugin architecture allows indep developers to enhance the feature of a product without requiring a release or and update to include that plugin. A devloper can just install the plugin and integrate with the product.
Good examples is WordRMR or OOo FBTool
that plugs into OpenOffice.