Anyone with a smart phone will be instantly familiar with "apps," the small applications and programs which run on the phone. Originally they were nothing more than simple games or labor-saving functions, but now they are omnipresent and highly useful pieces of software. Since smart phones have simplified interfaces and limited graphical and processing capabilities, apps have become essential for replacing what would normally be accomplished by other pieces of software, such as RSS feeds, browser interfaces, or executable programs.
As such, if you want your customers, clients and followers to be able to do anything more than just visit your website on their phone, you will invariably need to provide them with an app. Apps can be very simple (lists, announcements and Twitter feeds) or very complex (phone tools and games) but the primary reason that your company or website should have an app is so that your customers, clients and followers can keep track of what you have been up to on their own time, when they want to. Alternatively, your app may be a fun game or useful utility that is sponsored by your company, in which case the goal should be to entertain or assist the user while reminding them of your own products and services.
The best app is one which is simple, direct, and has clear intentions and objectives. It is not a good idea to try and copy someone else or be the next killer app. Instead, try to find one thing, and do it well. If your website sells a product, have your app announce new items, the latest deals, and update users with reviews of products they intend or might want to buy. If your company produces calendars, consider a simple calendar app with a reminder that they can get physical versions at your shop. If your company produces stationary, processes photographs or sells paintings, a background-changing app might be a good deal.
In any event, the app should be free, simple and unobtrusive. People are quickly annoyed when their phone constantly rings or vibrates with updates that aren't immediately relevant, and will delete an app which is not useful and takes up space. Therefore an app should use little space and should only try to get the customer's attention in ways they have chosen. Allow them to choose to have it update their calendar, send them an e-mail, or otherwise give them the information they want in a time and place that they want it. An ideal app is one which helps a customer so quietly and agreeably that they only notice it when they want to.