The very first road to the various app stores from Apple and Google was paved with native code. If you wanted to write for iOS, you learned Objective-C. If you wanted to tackle Android, Java was the only way. Similar issues popped up with all the other smaller players in the smartphone market.
Then some clever developers came to a realization: All the smartphones offered a nice option for displaying HTML in a rectangle on the screen. You have to write a bit of native code that pops up this rectangle in the native language, but everything inside the rectangle is controlled by the same languages that control the browser.
That started changing several years ago. Apple relented and recognized that HTML was not dangerous. Then the hardware got faster, smoothing over many glitches. Today, some of the HTML-based apps I've been writing perform just as well as native apps — and they're much easier to port.
PhoneGap began as an open source project before it was absorbed by Adobe. There's still an open source version called Cordova available from the Apache Foundation and a very similar version called PhoneGap that's available under an open source license (ASF).
The principle difference is that Adobe offers a smooth Web service that turns your HTML into apps. You write the HTML, and Adobe's cloud turns it into something that runs on iOS, Android, Windows Phone, BlackBerry 5/6/7, and webOS. There's a free version that lets you build an unlimited number of open source apps, but only public apps. Professional developers can pay $10 a month for unlimited private apps.
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