OS X 10.9 Mavericks includes an iBooks app that allows you to read any documents - including purchased books or your own pdfs - that you had in iBooks for iOS.
Mavericks is a free upgrade available for the following systems, and was released on 22 October, 2013 through the Mac App Store.
From OS X Mavericks : System Requirements
To install Mavericks, you need one of these Macs:
iMac (Mid-2007 or later) MacBook (13-inch Aluminum, Late 2008),
(13-inch, Early 2009 or later) MacBook Pro (13-inch, Mid-2009 or
later), MacBook Pro (15-inch or 17-inch, Mid/Late 2007 or later)
MacBook Air (Late 2008 or later) Mac Mini (Early 2009 or later) Mac
Pro (Early 2008 or later) Xserve (Early 2009) Your Mac also needs:
OS X Mountain Lion, Lion, or Snow Leopard v10.6.8 already installed 2
GB or more of memory 8 GB or more of available space