The level that a few guys mentioned is really cool. The one I use will look like a standard level if you hold the phone on its edge, and when when you put the phone down on its back, it becomes a 360-degree level.
Also, we found an altimeter app, which is very cool in the mountains if you have a partner who can watch the numbers change while you pay attention to driving.
Both of these are android apps.
2013 Surveyor SP220
2010 Silverado LT 5.3 V8
The world is a great book, of which those who never stir from home
read only a page. - St. Augustine