Your app's shelf life on a user's Home screen is exactly as long as it can hold that user's attention. iPhone owners chew through apps, gulping down their content, then tossing them out and moving on. Apps with a fixed amount of content or data are particularly vulnerable to getting jilted; once your users read your ebook, play all the levels of your game, or flip through all the flash cards of your vocabulary builder, there's nothing left to keep them around. If that's your intent, that's fine; some apps simply have a limited lifespan, and once the content is exhausted, that's the end. But if you're trying to create a long-term relationship with your audience, your app has to keep giving. It has to have a heartbeat to stay alive and remain tapworthy.
Certain kinds of apps have a built-in heartbeat thanks to the fundamental nature of their key features. Tools that organize personal info (to-do lists, calendars, expense trackers, contacts) keep people coming back as often as they need to check an appointment time or add a reminder to pick up the milk. Likewise, utilities that perform a common task (Skype calls, instant messaging, barcode scanning, weather forecasts, notebooks) continue to be useful as long as the underlying task itself is in demand.
For most of us, tools and utilities still account for the majority of our desktop software. Most folks use computers to work . . . to do. That doesn't hold so true for iPhone apps. Instead of tools, the majority of apps in the App Store are some flavor of content app—games, entertainment, books, references, novelty apps. When we use this category of apps, we're consumers, not doers. When there's nothing left to consume, we move along to a new app. For these apps, it takes more work to keep the heartbeat thumping. Sometimes that simply means fresh content. News apps, of course, have a bottomless and constantly refreshing reservoir of news, drawing users back regularly for more about the latest political brouhaha or Brangelina update. For these apps, as long as the content continues to appeal, users keep coming back.
Non-news content apps have to be a bit more creative, but the challenge is the same: to continue to provide fresh content. Games can offer additional levels through in-app purchases, which also has the happy side effect of steering additional cash into the company checking account. But new game levels are about more than just an opportunity to keep playing; they're markers of achievement. You've beaten the game and you're ready for more, even ready to pay for more. There's a collect-em-all mindset, and the game grows as you get better. That approach might seem unique to games, but other types of apps can offer a similar sense of expansion as achievement, letting you unlock new content as you master various chapters, challenges, or lessons.
Figure 2-19. In-app purchases and add-ons let users keep the good times rolling . . . literally, in the case of the Skee-Ball-themed game Ramp Champ (left), which lets you download new ramp themes for free or fee. Skies of Glory, an aerial combat game (above), lets players upgrade the game's gear for a fee. Here, a Zero plane will run you three bucks.
Travel apps are especially road-ready examples of apps that benefit from content that expands and adapts to mirror users' activities. Lonely Planet Travel Guide, for example, comes with a single city guide to San Francisco, but offers scores of other travel guides and phrase books for purchase inside the app—buy a new guide when you're headed to a new city. The app's content collection expands according to your needs (and pocketbook), so it stays as fresh as your arrival in a new city. This collection of destination guides meanwhile memorializes your globe-trotting meanderings as readily as stamps in your passport—or vanquished levels in a game. Similarly, OffMaps lets you download maps and guides for off-line use anywhere in the world, handy for dodging international roaming fees that otherwise make it ruinously expensive to use the built-in Maps app abroad.
Figure 2-20. Travel apps can expand their content as you expand your travel horizons. OffMaps (left) lets you download maps as you need them. Lonely Planet Travel Guide (right) offers new guides for sale inside the app, ready when you arrive in a new city.
This steady unlocking of content is also a staple of fitness apps. CrunchFu, for example, is an app for acolytes of the six-pack ab, a training program to help transform bellies from wishy-washy to washboard. The app gives you a daily training program to do a recommended number of crunches. As you complete each day, you unlock the next day's program, each one gradually more difficult until you finally gut through 200 crunches at a single go. These steady, game-like accomplishments keep users coming back while also encouraging a safe fitness ramp-up, an effective way to give the app a healthy heartbeat.
Figure 2-21. CrunchFu keeps users coming back with its progression of gut-busting training programs. Even when the program is done, though, the app's head-to-head "crunch battles" maintain interest.
Even so, CrunchFu's content is limited by the fact that its training program has a finish line. After you hit 200 crunches, you're done. Normally, when users finish an app's content, they'd amble off into the sunset, never to look back at the app again. Once again, though, gameplay saves the day. Even when the training program peters out, CrunchFu provides a game to hang on to some portion of its users. The app offers "battles," head-to-head crunch competitions with other CrunchFu users. No matter where you are in the training program—beginning, finished, or somewhere in between—the app lets you find someone else at your fitness level and challenge them to see who can do the most crunches, earning points as you go. Human contact for the win!
It might not look like it as we tap away at our iPhones, off to ourselves and oblivious to the world, but we are irresistibly social creatures. iPhone or not, we're drawn to activities that let us communicate, compete, or contribute. Like a physical place, apps that bustle with the activities of other people feel alive. Community features give an app life beyond its fixed set of content. Even after you've mastered a game, the chance to test your skills against other players gives you an incentive to keep playing. For other apps, sharing content with friends and seeing what others are saying lets your users provide an ever-replenishing supply of fresh content. Among its many other features, for example, the Movies app by Flixster pools reviews by regular-Joe moviegoers. You can follow the advice of the grand mass of public reviews, or just listen in on what your friends have to say. Yelp adds similar value by encouraging customer reviews for local businesses, and Amazon, of course, does the same with reviews of its products. In all of these cases, community-driven reviews give extended life to the basic content provided by the app developers.
You don't have to build this stuff yourself; you don't even need your own community. Just plug your app into the established social networks, where millions of people are already talking. Facebook and Twitter both provide easy platforms for sharing content from iPhone apps. For games, social networks like OpenFeint or Apple's Game Center let developers plug high-score leader boards and head-to-head challenges into their apps.
The idea is to wrap secondary features around your app's main content to enhance and extend its value. The apps described so far have done this by growing or sharing that primary content. But another effective, if less elegant, approach is simply to bolt on complementary tools. The Typography Manual, for example, is an app for budding graphic designers. It's essentially an ebook spelling out the history of typography, tracing its letterforms and laying out its technique. While the app does a fine job of dotting the i's and crossing the t's of its subject, it remains like any book, a fixed set of words and images. But the app also throws in a handful of tools that are useful to folks who sling type for a living. There's a font ruler, some font-size calculators, and a comprehensive reference for easy-to-forget HTML codes for special characters. Even after users finish reading the book, these add-on utilities keep them coming back by continuing to provide some modest value.
Figure 2-22. In addition to its reference content—a visual typography glossary (left), an ebook, and an HTML reference—The Typography Manual includes a font-size calculator (middle) and a font ruler (right) to provide lasting utility even after you've consumed the app's content.
As with all things iPhone, however, use restraint. Think hard about the features that can give your app extended longevity, but don't just pad the app with features willy-nilly. It's often a useful service to your audience to design your app for a steady, long-lasting heartbeat. But as you do this, it's even more important to keep the app simple and focused.