XDA user x2kjosh got curious about what exactly his phone was doing at any given time, as I'm sure we all have at some point. Your GPS icon randomly showing up in the task bar is a perfect example: What the hell is it doing there? What app is getting my location? Obviously tired of all the questions, Josh wrote a handy little app called Task Identifier.
The idea of it is simple: Notify the user whenever an app is loaded into memory. It's a pretty straightforward concept, but it is actually really interesting to use. It's hard to explain, so I'll just put the description for the thread and some pictures here: