Olivier Goguel of the Apple II demo group FTA has released the iOS source code to his Apple IIgs emulator, ActiveGS. ActiveGS was in the App Store wrapping a number of FTA demos, but Apple finally pulled it (long ago).
Now, anyone w/ an iOS device can download Xcode 7, compile, and install this emulator on their iOS devices. Instructions are simple and provided.
I made a demo video of ActiveGS (I had a dev build from Olivier directly) a few years ago on my iPad 2. Have a look:
And my post on the initial App Store release of the aforementioned demo collection: