Well that all depends on what you are looking for.
For
Stage Managers, apps that I've found useful are a simple PDF editor, you can scan in your script then you can type notes, highlight lines, insert pics, really anything you want. then you can email out, or print script updates very easily. On the more expensive side there is a great app called
stage write that you can use for
blocking and scene shifts. You can even animate scenes so the pieces move around.
For lighting,
ETC makes an
iRFR app to connect to your
ETC console, which allows you to control playback, do
dimmer checks, and follow playback in real time and take notes on cues. Also there is Touch
OSC to connect to other consoles. Lightwright makes an app that connects with the computer version to update paperwork on the fly. Barbizon has an app version of their Electrician's handbook that is very handy. Both
Rosco and
Apollo make apps for their gobos. There is also a great app called
gel swatch library that lets you look up and compare
gel from all the major companies. Also as a student you can get free versions of Auto-cad and
Vectorworks to do drafting, another free drafting tool is Sketchup. You can use all three of these with stagewright to import
ground plans. There is an app called Lampy LX that can help with basic
power calculations,
dmx addressing, and many other basic functions within lighting.
These are just a few of the apps out there that can help you.