
mScrob is a lightweight Last-FM Scrobbler. It works in conjunction with the iOS build in music player, and Scrobbler either in realtime if the app is running, or songs played since last run when you run it.
Latest Update
It has now been updated for iOS 9, and also runs on iPad.
Get it here:
https://itunes.apple.com/us/app/mscrob-free/id633270086?mt=8