1. Carpenter’s Square

Sure, the iPhone’s not big enough to replace a real carpenter’s square, but it kicks the crap out of “that looks close enough” when your square is miles away back in your toolbox. In the picture above I was building a bit of impromptu signage (read: an 8′ tall stand to hold a banner). The result: close enough that it stood straight even in some pretty stiff wind.

2. Short Straight Edge

Again, it’s a bit small to replace a ruler or yardstick. But if you need to scribe a line across, say, a 2×4, it works fine. Just remember to use the side without the volume control. Note: If you end up with a few scratches on the back of your iPhone, wear them with pride. At least you’re_ using_ your phone, right?

3. Bubble Level

This $0.99 app from CirkelSoft leverages the iPhone’s accelerometers to turn it into a fairly effective bubble level. The downside: you need to calibrate the app first with a real level to give it any accuracy. But after calibration it’s always there with you, even when you show up at a friend’s house to hang shelves only to discover that he doesn’t own a level. Doh!

4. (Sorta) Poor Man’s Dynomometer

Want to know for sure if that cold air intake or chip really makes a difference in your car’s 0-60 time? You could spend $200 for a G-Tech Pro Performance Meter (or a ton more for a real dyno session), but the $13 Dynolicious app gives you pretty damn similar data via a device that’s already in your pocket. Besides capturing and displaying various speed and acceleration tests (0-60, 1/4 mile, etc.), it also records and displays lateral and braking Gs — including a real-time graphical skidpad display — and can estimate your vehicle’s horsepower by factoring in acceleration and weight.

5. Shop Camera

Any camera phone works for snapping quick pix of an item before you take it apart. But unlike most camera phones, the iPhone allows you to pinch-and-pull to zoom in photo detail. Combine this with a pretty large screen (as cell phones go) and the iPhone becomes an asset when you’re re-assembling drum brakes or trying to remember which wire went where behind a car dash