OverDrive was just sold by Rakuten (Kobo) to KKR (a private equity firm). KKR also owns RBmedia, the parent company of RBdigital. Now that they're all under the same umbrella,
OD is acquiring RBdigital in order to merge all of the library assets into one entity. What happens next remains to be seen.
Please see this thread for additional discussion --
Overdrive to Acquire RBDigital.