Two years ago, as part of a few groups I was involved with, I organized a series of student talks for the university community. One of them was presented by Jason Brennan, who spoke on iOS development. I was planning on spending that Christmas break to learn something new, but it was that talk that convinced me to learn iOS specifically. In addition to extolling the virtues of Objective-C and Cocoa Touch, Jason talked about changing the world, saying something to the effect of "if you're not writing software to change the world, get out, because you're doing it wrong." At the time I thought it was effective presentation rhetoric (that's a compliment). Looking back, maybe not.
Let's look at what I've been doing lately.
The app I'm writing for UNB, my alma mater, is being used to help recruit new students into a good university and relieve tedious tasks off already overworked systems support staff. Previously, they would transcribe handwritten entries into their database. Now, the iPad app lets them import a spreadsheet, saving hours of effort.
I wrote a Solar System simulation as a class project and later put it up on the App Store. Now, there are elementary schools in Australia using it to teach kids about our Solar System.
Most recently, I've developed an iPad app for 500px, an online community of aspiring and professional photographers. The iPad app lets people see amazing photos from all over the world in a way that's not possible on a regular computer.
Maybe only in small ways, I feel like I'm changing the world, but that feeling is why I get up in the morning. I feel really lucky that my profession lets me doing the kind of really cool things I get to do.