The best Game Boy Advance emulator for iOS is available now, no jailbreak required.

Independent developer Riley Testut released on Wednesday a long awaited update to his polished Game Boy emulator, GBA4iOS, and it's far and away the easiest and best looking way to power up your childhood nostalgia and do some classic Nintendo gaming on the iPhone. The emulator now supports Game Boy Advance, Game Boy Color, and original Game Boy games.
Beyond its game playing capabilities, the 2.0 update contains all new features, a refreshed design, and, as was the case with Testut's previous effort and the primary source of its notoriety, it can be downloaded on any iPhone or iPad running iOS 7 without needing to jailbreak the device. All that's required is to open up Testut's dedicated GBA4iOS Web site -- which greets you with the sleek, Apple-inspired message, "Game Boy Advance, meet iOS. Again" -- and tap "download."

Super Mario Advance 4: Super Mario Bros. 3 being played on an iPhone 5S using GBA4iOS 2.0.

(Credit: Screenshot by Nick Statt/CNET)

Throughout the nearly two years the high school senior and current Texas-native has spent building out and refining the emulator, Testut has managed to enlist a growing group of fellow designers, developers, and fans to help him fine-tune the project, including a graphic designer, a tech support specialist, fellow emulator creators, and a healthy group of beta testers. And it shows.
The app now matches current iOS 7 design schemes and comes loaded with a slew of other features. There's dedicated portrait and landscape modes for both Game Boy Advance and Game Boy Color, an autosaving function, downloadable controller skins, easy-to-access ROM downloading and saving, and generally the kind of smooth functionality you'd expect from a paid iOS app in the App Store, including some impressive game-specific features for titles like Pokemon.

(Credit: Riley Testut)

Testut has always released GBA4iOS and its updates for free and has no intention of monetizing his efforts at the moment.
GBA4iOS and the iOS overlord
GBA4iOS made headlines last year when it was discovered that Testut was able to bypass the App Store entirely and distribute his emulator to any iOS device, jailbroken or not. By having a third party -- in this case the company MacBuildServer -- approve any device demanding a download with its own enterprise certificate, all that was required was for one to click a single button to automatically compile the app via GitHub and then have MacBuildServer sign off on it for his or her particular iOS device. Then it showed up on the home screen.
Because by enrolling in Apple's iOS Developer Enterprise Program, MacBuildServer built its developer-focused business around easily putting any app on any device but hadn't exploited that particular loophole on such a grand scale until GBA4iOS.
The enterprise certificate is supposed to allow companies to limitlessly install a beta version of an app on in-house devices, presumably for testing. So when GBA4iOS blew up, Apple quickly brought the hammer down and MacBuildServer was forced to sever its association with the publicly distributed emulator.

I've prepared for this and found a way to still update the app even once Apple shuts it down, if they do." --Riley Testut, GBA4iOS developer

But the app lived on, though each and every time the app needed to be reopened, it required users to set the date on their iPhone back before the expiration date of the enterprise certificate MacBuildServer used to authenticate the download. Testut released the emulator through another site, iEmulators, and began openly documenting his progress on GBA4iOS 2.0 on his blog.
"But how am I going to release it now that MacBuildSever is dead? For now, that's a secret. But I can say it definitely will not require a jailbreak, and it will not exploit a security bug in iOS (as jailbreaks tend to do). It will be as simple as tapping a button on your iOS device and installing, just as before," he wrote in August of 2013. And, as promised, the app has arrived with the one-button download ease Testut had hoped for.
Testut won't say exactly how he's distributing the app this time around, for obvious reasons. "As for distribution, it does use a method very much like MacBuildServer; an enterprise certificate is being used to install the app," he told me. "However, I've prepared for this and found a way to still update the app even once Apple shuts it down, if they do."
Opening GBA4iOS 2.0 issues a similar warning about having to potentially set your date back before February 19 if one runs into issues after restarting a device or quitting and reopening the emulator for any reason.
We've reached out to Apple for clarification on its stance on GBA4iOS and will update this post when we hear back.
Update at 3:15 p.m. PT: It appears Apple has already responded to the update by revoking the enterprise certificate being used by GBA4iOS, according to Testut on Twitter: