We've covered GENWI before, but to recap: GENWI is a cloud-based (read: Web) app creation and management system for businesses. While there are numerous platforms and 3rd party services which will "wrap up" your content into a native app, GENWI does all of this on the web, and it's a pretty compelling service.
You can also create HTML5 mobile apps, but the native app tool is likely more interesting to publishers. GENWI also allows you to update your content live via their tools. Pricing is US$99/month for web and smaller-screen usage, and you'll need to have a developer account to publish these on the App Store. If you want to deploy an iPad app, however, the cost jumps to $499 per month. Be sure to see it in action below.