It says "while supplies last" (banner on the Kobo site about 2/3 down the main page) so I don't know how long this is good for, but Kobo has a "deal" right now where if you install the Windows 8 app you get a free copy of
Robert Ludlum's The Janson Command by Paul Garrison. I just installed the Win 8 app and logged it into my Kobo account and sure enough the book appeared in my account. Was able to download an Adobre DRM'd copy from my library on the website just fine. As far as I know this offer is US only.