iPhone devices started the smartphone craze which would go on to replace conventional mobile phones in both Japan (which had its own subset of cell phones) and the rest of the world, with more advanced touch-controlled devices.
Unlike their direct competitor, Android-based smartphones, they have currently no usable emulators, as the official iOS SDK (macOS-only) only allows for running your own projects, i.e. they run code generated for an x86 target rather than ARM code as used by iOS. However some emulators e.g. BlackThunder, make use of such simulator in iOS SDK to run few chosen iOS apps that are recompiled for x86.
History of Failed iOS Emulation Attempts
Many of the currently available "simulators" only try recreating popular iOS apps (like browsers) in a PC application with no real emulation involved. Some notable scams in such fashion are called iPadian or variations on the name, and are often malware.
- A project to emulate various smartphones (iPhone, iPod Touch, iPad, Apple TV 2G) called iEmu, started in 2011 but got mysteriously abandoned two years later before anything usable surfaced. All pages related to the project were removed. It's speculated Apple had a hand in this.
- Nowadays, a malicious APK file going by the iEmu moniker is also being circulated on blogs run by script kiddies claiming to offer a way to run iOS apps on Android. More often than not they're uploaded with the intention of generating revenue from impressionable users (through pay-per-click URL shorteners) who fall easily for those types of scams.
- There has been recently a project to provide a runtime for iOS apps to run on Android called Cycada (formerly known as Cider), but not much progress has been made as of recently, and the original author was accused by some of being a sellout for leaving the project to work as a kernel programmer for Apple.
- There was also a project based on QEMU that usually went around by the name QEMU-s5l89xx (based on the part number of the original iPhone), or iVM. The last known commits to this project were in 2013, and it is unclear if this project will ever come to fruition.
Your best bet, until a new emulation effort is ever started, is to hope for whatever iOS app you are interested in, to have an Android port. Which is often sadly not the case (until very recently) for the vast majority of the older game apps, especially Japanese ones - as the Android is perceived often to be the more piracy-friendly platform. That appears to be gradually changing lately and isn't as much concern for non-gaming apps, but the older apps are unlikely to get ported for the most part.
iOS apps are distributed in the IPA format. Like its Android counterpart, APK files, they can be opened as a regular zip file most of the time and their contents dissected this way.