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If you and/or your nephew are up for a rather steep learning curve then Blender 3D Modeller can make excellent 3D castles, with walk/fly-throughs, animations, and just about everything on your list other than AI driven attacks. Blender itself is available 100% free for Windows, Mac & Linux. A little research online will also give you at least one blender ...


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You could always create your castles within Minecraft for which there are castle creators, online video training and even workshops from English Heritage. Minecraft is available for a number of platforms including Windows.


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Try researching "decision-making software". 1000minds is the biggest in this space.


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Ben Eater has made a video series of building your own 8 bit computer, explainaing all the parts. Many people have built that computer, but one guy took it a step further and wrote an emulator and simulator. It's available online for free The famous 6502 CPU is a lot more complex, but it's available as Visual 6502 as well. I'm not sure if the 65C02 Simulator ...


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