Castle Game Engine is now integrated with the Apple Game Center on iOS! The new TGameService class handles both Google Play Games (on Android) and Apple Game Center (on iOS) with a common API.
A working example is within the
examples/2d_dragon_spine_game/, in particular see the Game.pas that implements the game logic and achievements.
Also, CastleMessaging unit was ported to iOS (this is used by various Android/iOS services), and various other “infrastructure” changes were made to enable implementing “services” nicely on iOS.