As the title reads. Recommend an app and tell us why. Has to be a mobile phone app (Android, iOS ect) I'll start. iStudiez Pro (Thanks to VP for it) Keeps me on schedule with my homework and school.
Obligatory Angry Birds referral. Defender & Lair Defense from DROIDHEN. Great time sinks and entertaining games. DiceBag and Combat Assistant are immensely helpful for running my RPG from my phone when away from my PC for long periods. (I DM an online adventure)
pdanet for android use your 3g/4g connection by connecting your smartphone to your laptop via usb, so it doesnt drain out of power gasbuddy for android finds cheap gas near you