App success stories aren't just about the many millions of downloads seen by Angry Birds, Facebook, Doodle Jump and other big hits.
Further down the apps food chain, there are many more stories of developers whose numbers are less headline-hogging, but who are still making a good living, and exploring the creative possibilities of apps.
A good example is UK app Rockford's Rock Opera, which started life as an enhanced audio book three years ago, but has since spawned a pair of iPhone apps and notched up more than 30,000 downloads on Apple's App Store.
Created by UK couple Elaine and Matthew Sweetapple, working with comedian Steve Punt and a developer Apache Solutions, it is going toe to toe with book apps from big brands such as Disney, Dr Seuss and Star Wars in the upper reaches of the UK App Store's paid-book apps chart.
"It's genuinely homegrown: it's made at home!" says Sweetapple. "The pictures are done on the kitchen table by my wife Elaine, and the audio is created upstairs. It's not Pixar or Disney, but people can see it's made by people who are in love with what they're doing."
The rock opera has an educational and ecological theme, based on an island that is home to extinct animals, who have a message for the world that gets delivered by a boy called Moog and his dog Rockford. The World Wildlife Fund is a supporter of the project, whose audiobook has been downloaded more than 1 million times and been used in more than 15,000 UK schools.
The audiobook has been split into four parts for iPhones. The first (free) app was launched in December 2009, with the second episode following in October 2010 for £2.99. The final two episodes are due out this spring, with Android and iPad versions on the way soon.
The Sweetapples have spent nothing on marketing the apps, which have steadily risen up the App Store charts on word of mouth and positive user reviews alone.
The first episode has been downloaded more than 25,000 times, while the second has generated more than 5,000 paid downloads, meaning net revenues of more than £10,000 to fund the production of episodes three and four – both Sweetapples have other jobs, so this is not their only income.
Matthew says the apps have brought in a new audience for Rockford's Rock Opera. "Rockford is key stage 2, so aimed at six to nine-year-olds, although we've always thought it was absolutely for a family audience," says Sweetapple. "But iPhone has taken it so much younger: people write us emails saying their 18-month-old loves it."
He also has strong views on the musical content, contrasting Rockford with some of the cheesier children's apps on the App Store.
"Parents get driven mad by plinky-plonky music for kids, but it doesn't have to be that way," he says.
"I loved the Beatles when I was two, and if you look at some of the best songs, they're incredibly simple and almost nursery rhyme-like. There's no reason why music that children can like and sing along to has to be obnoxious to adults."
Once all four episodes have been released for iOS and Android, Sweetapple says that he and Elaine will weigh up the merits of other platforms, such as BlackBerry. He seems keener to start making spinoff apps, though.
"Our intention in the future is to do some apps that make far more use of iPhone's functionality," he says.
"There's potential for games, or maybe even augmented reality apps for children to interact with these animals in the real world. It's clear that apps are a fantastic way of delivering enhanced audiobook content, but we want to do more."
One last thing: how did Punt get involved? It turns out he and Sweetapple went to school together. "We were in a band together at school, and always wanted to do a rock opera – all our songs were mini operas," he says, before pausing and chuckling. "We were a very pretentious band, I suppose!"
