BillPin for iOS is easy to use to split bills and then keep track of who has paid up, especially among Facebook friends. You can also let friends know what their share of the bill is via email. The app splits bills evenly, or can make adjustments if some of those who are sharing the expense need to pitch in more than others. The app present a summary along with a record of all shared expenses.
If you used Billmonk in the past, you'll want to try BillPin, which also offers a free Billmonk backup service.
BillPin supports 40 currencies, including BitCoin. The BillPin iOS app syncs with BillPin online expense sharing.
iOS Compatibility: iPhone 3GS, 4, 4S, 5 / 5th generation iPod touch / iPad / iOS 5.0 or later / Optimized for iPhone 5
Download iTunes app store: BillPin