The new app supports Chrome, Safari, Firefox, and Internet Explorer. It enables users to download and read .Book (XMDF?) and Epub ebooks purchased from Booklive, including both manga and reflowable text.
There aren't any early user reports yet, but my source does note that users are limited to downloading a single title at a time, which can be read offline.
Booklive is one of the smaller ebookstores in Japan, and it is owned by a coalition of Japanese tech companies which includes Toppan, NEC, Toshiba, and others. A recent survey put Booklive in 6th place in terms of popularity with the Japanese ebook buyer. In addition to reading apps for iOS, Android and Windows, Booklive has also released the Lideo ereader in December 2012.