The aim of Calzone is to create a Javascript library which can be dropped into EPUB files to greatly improve the typographic experience of ebook readers. Most current e-reader software does not support lovely typography. In particular, there is little if any support for hyphenation, paragraph-level justification, keep and break controls, and other typographic necessities in a reflowing ebook environment. (See http://johndberry.com/blog/2012/03/06/what-is-needed/ for a full list of gripes.)
But the EPUB standard, in particular EPUB3, grudging allows for readers to support the execution of JavaScript, and many e-reader software already executes inline Javascript in EPUB files. Which means that the programmer already has a lot of control over what gets displayed on the page.
Borrowing (extremely) heavily from http://www.bramstein.com/projects/typeset and http://search.cpan.org/perldoc?Text::Hyphen , Calzone fills in the gaps that reader software leaves behind, fiddling with the placement of words and paragraphs on the page to make e-books prettier.
There's nothing particularly EPUB-specific about Calzone, so if you like you can use it to improve the typography of ordinary web pages too. I wouldn't, though.
See http://simoncozens.github.com/calzone/ for a rigged demo.