One of the biggest things many users with jailbroken phones have to explain to other folks is which third party applications are useful. Yeah Pirate is cool, and Navizon makes the lack of GPS slightly more bearable, but what really takes the iPhone beyond what Apple has provided in a useful way? To me, a little over a week ago, the answer came in the form of a downloadable app called Level that makes use of the iPhone's accelerometer to give users a quick and dirty (yet eerily accurate) recreation of a spirit level--the things people use to make sure pictures are straight, and whether or not a surface is properly flat. Most of you have probably seen some of the early iPhone apps that would let you see which way the accelerometer was pointing. In many ways Level manages to do the same thing, albeit with a little more grace. Amid the barrage of Holiday advertising, you're bound to see ads about new and improved laser levels that can do everything but make you sandwiches, but what about for everyone else who just needs a quick way to make sure something is reasonably straight or flat? The app manages to do just that, and with a surprising level of accuracy--although if you have a properly calibrated level at hand, you'll notice it can be a tad off depending on what side of the phone you're using. For that reason, it's probably best to stick with a good old fashioned level you'd pick up at the hardware store. Level is a part of iApp-a-Day project done by SpiffyTech which reaches its conclusion on Friday. We wrote about it last month, and since then they've put out 27 different apps including, productivity tools, the absurd, and even things that creep us out. Note: This post was written by Josh Lowensohn, Assistant Editor at CNET.com. You can find the rest of his stuff on CNET's Web 2.0 blog Webware.com.