CitriOS is a 3DS emulator built on Citra for iOS and iPadOS.
It is written in C++ and based on Citra's code.
The emulator itself is not out, but you can try it out by taking the build from the latest Github Workflow (or Nightly.link
Citra (base) is licensed under the GPLv2 (or any later version). Refer to the LICENSE.txt file.