Carx and forza horizone 3
Welcome to the community. 
What about them? Your post offers very little information as to its purpose.
Are you suggesting trainer for them? If so, no, they will never happen.
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Carx: Is an online multiplayer game. Trainers are for single player games for technical, moral and legal reasons. See: CarX Drift Racing Online Cheats and Trainers for PC - WeMod.
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Forza Horizon 3: The developers will ban anyone who cheats in this game, even in single player. Therefore a trainer is pointless. See: Forza Horizon 3 Cheats and Trainers for PC - WeMod.