Remember GBA4iOS? It was a gameboy advance emulator on iOS that used a AppStore enterprise bug to bring emulator to everyone without a jailbreak. Apple closed that bug but now its back with version 2.0 and the website has a countdown which will finish tonight.
From site:
How can I install GBA4iOS?
Unlike other apps for iOS, you can not install GBA4iOS from the App Store. Until GBA4iOS 2.0 is released, you can download version 1.6 from iEmulators, run by Start3rs, an awesome group of people who are beta testing GBA4iOS 2.0. To install, open the link on your iOS device, and follow the instructions at the top of the page.
It seems like they are using iOS Enterprise distribution. It'll work fine until Apple finds out and blocks their signature and shuts down their developer account.
Edit: Also be adviced that this means Apple hasn't screened this app for malware and privacy issues.
From site: How can I install GBA4iOS? Unlike other apps for iOS, you can not install GBA4iOS from the App Store. Until GBA4iOS 2.0 is released, you can download version 1.6 from iEmulators, run by Start3rs, an awesome group of people who are beta testing GBA4iOS 2.0. To install, open the link on your iOS device, and follow the instructions at the top of the page.