Alongside numerous other improvements, Apple updated the Calendar app in iOS 7.1 with a new split view. Fortunately, jailbreak users won't need to update to iOS 7.1 to get the new feature.
Ryan Petrich posted 'Gregorian' to his beta repo today. Gergorian is essentially the iOS 7.1 Calendar app which installs as a standalone application rather than a tweak to the existing app.
You can install Gregorian for free by adding the http://rpetri.ch/repo repository to Cydia.