Are you musical? Own a guitar or similar? Tuner for BlackBerry 10 could come in rather handy for you. As the name suggests it is a simple instrument tuner that utilizes the microphone on the BlackBerry and shows you which key the noise is in.
This is the free version of the application and for basic tuning this one suits me down to the ground. Purchasing the full edition can be done from within the app and only costs £0.75/$0.99.
If you do want to upgrade you can take advantage of the following features:
Although I do have a couple of guitars (which I don't play very often) this application is certainly going to replace the alternative methods that I have been using over the years. It may be basic but is sure is a sweet utility app to have on your device.
If Tuner looks of interest go grab the free version and see how you get on.