You can try Sweet Home 3D.
It has both desktop and web-based versions. It's free and open-source.
It's pretty straightforward on basic planning. If I remember well, you can create multi-floor projects as well. It has some in-built furniture and there are some other furniture libraries available both on the website and from some manufacturers.
Two classical open source options are Inkscape and Scribus. I've used both to make pamphlets etc., and both run on Windows, Linux, and macOS.
Inkscape is a versatile vector graphics editor. It is fairly easy to get started with, but has a lot of advanced features. You have all basic shapes, polygons, line and fill styles, basic text, layers, effects like ...
Honestly, your example illustrations were all top-down vector graphics, such as can be done in Adobe Illustrator, Affinity Designer, or InkScape or Xara.
I don't think you need full-on 3D modeling, though if you do, Blender is a really great tool as mentioned before by @Steve Barnes. I fully second his recommendation.
Adobe Illustrator is an industry ...
I would suggest that if you are prepared for a somewhat steep learning curve you consider looking at Blender 3D modelling tool. While it might be a little overkill for what you are currently doing, (i.e. Plan View only), you can model your roads, intersections, etc., on a single plane initially and consider adding a 3rd dimension later.
Free, Gratis & ...
After some thought, I ended up creating a full complex pattern using an Excel spreadsheet.
I feel tremendously badass for having accomplished a task I thought I'd have depend on some CAD software and personnel who can work with it.
For anybody else that ever comes across this need and is looking for a solution, here is the spreadsheet: http://files....
Perhaps you should consider GraphViz?
You write simple text files, then run therm though the tool to draw diagrams of various sorts. Here's their example of a (very large) network (there are many more examples in their gallery).
Note that the input text file was generated by a network scanner tool. I have often coded similar programs to generate the ...
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 ...
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.
Another possibility is BricsCAD Shape. It is free and there are good tutorials on the site. I will say if you have a lot of experience with 3D solid modeling it might actually be harder to figure out BricsCAD Shape. It works differently than I expected, but looks like it is pretty capable. It isn't strictly an architecture modeler, but seems pretty slanted ...
Provides rich functionality around a drawing <canvas>.
Objects (shapes) can be moved, scaled and rotated. Text fields and images are such objects, for instance.
Drag and Drop with canvas-external objects can be easily implemented. I've once done it with images which can be moved onto the canvas via the mouse.
Loading the state from JSON and ...
It depends on what technology stack you want to use long term.
Back in the day, I would simply use Visual Studio to develop my wireframes, which allowed me to transition from wireframe versions to functional software very quickly.
I recently worked on a project where the designers used Invision. So I didn't create the designs, but I was able to comment on the designs and make change requests. The designers were not developers and only did interface design and mockups with invision.
So you could do a mockup without programming anything and present the basic app to investors.
Take a look at Adobe XD. It is a drag-n-drop prototyping application for mobile apps and websites. It is intended for designers that have no programming experience, and it really is amazing how powerful it is for creating a professional prototype.
Adobe offers XD for free, so you can download it and do the tutorial. You'll see how easy it is to make ...
WordPress is a great framework to start with and is likely a perfect fit for your situation.
The following link is an article describing six great online coursework plugins for WP, most of them free. The free ones are available directly from wordpress.org, which means they have been vetted and tested by the WP community.
Online Course Plugins
The next ...
You could almost certainly produce your display with python, ipython notebooks, (Jupyter), and bokeh, your notebook can poll the data from any suitable locations and could be viewed either via nbviewer as a static page or as a dynamic page.
A nice example of the sort of thing that you can do is the Periodic Table example.
I'm a developer of windows alternative for xScope. You can try it http://rulerforwindows.com for free.
Create, layout and adjust custom marker boxes that float on top of all other on-screen elements.
Quickly and easily find the spacing between any point visible on the screen.
Magnify the area under your mouse preview color and the cross ...
I've used LibreOffice Impress as well as regular Powerpoint, where we've made stick templates of the appropriate size and orientation for students to put content into. This then gets output as PDF for the printers. Preparing the generic PPT is an effort but the consistency of output is well worth it.