While the new Slide Over and Split View multitasking views that came with iOS 9 can be useful, one thing you can't do is use two Safari windows side-by-side, and now Sidefari aims to fix that. Using a Safari View Controller, Sidefari enables this capability in a limited, though still workable, fashion.
With Sidefari, you open links pasted from your iPad's Clipboard in the app's Safari View Controller. Open up the Slide Over window or Split View, and you can view two webpages at the same time. You can also use the Sidefari's action extension to send your current link to the app without needing to copy and paste. You can also easily view your browsing history in Sidefari, which can be disabled or deleted.
Sidefari is available for download from the App Store now.