Delta is the successor to a popular GBA emulator, GBA4iOS, made by the same developer and started development back in March of 2015. Similar to RetroArch, it uses a core-based approach with each system running of its own core, however, it is not the same as Libretro format. So far only the NES, SNES, N64, GB(C), and GBA are supported with NDS emulation currently in beta and only available to Patreon donors. Support for Sega Genesis emulation is planned for after NDS emulation is publicly released.
Also read: Best Termux tools for ethical hacking and game hacking apps for Android.
Delta Emulator is supported on all iOS devices on iOS 10 or above, and the app has been specially optimized to support the iPhone X series of devices.