I'm one of those people that quite heavily customised their Windows 10 experience to run away from the actual Windows 10 as far as possible. I can confirm that Classic Shell (now Open-Shell) is 100% the one piece of software that makes Windows 10 usable. Having to use an unfamiliar Windows 10 machine with its Start Menu is jarring and unpleasant. The replacement Start Menu is just better.
Windows 10 Explorer has a couple of mods that change its functionality, but I guess that it could be replaced by a third party application entirely. There are both Explorer-style and Norton Commander-style (dual pane) file managers that would do the job just as well if not better than the stock application. Notepad and Task Manager also seem very easy to replace with freeware alternatives. I haven't tried such measures recently, but I can see no reason why they should fail.
If you want to mod away the Windows 10 taskbar (which is the one thing I actually like about Windows 10), you may want to check out RetroBar. It's a C#(?) replica of the classical-style Windows taskbar from 95 to XP eras. It even has the same icons and hides the original Windows 10 taskbar. It actually feels uncanny, running something so close to the real thing on such a new OS. It's very nice.
Other than that, I don't know of anything that would e. g. get rid of the new Control Panel or other mandatory parts. In practice, if you replace the things I listed above, it's really unlikely that you'll come across the stock Windows UI in the course of normal daily use.
Windows 10 Explorer has a couple of mods that change its functionality, but I guess that it could be replaced by a third party application entirely. There are both Explorer-style and Norton Commander-style (dual pane) file managers that would do the job just as well if not better than the stock application. Notepad and Task Manager also seem very easy to replace with freeware alternatives. I haven't tried such measures recently, but I can see no reason why they should fail.
If you want to mod away the Windows 10 taskbar (which is the one thing I actually like about Windows 10), you may want to check out RetroBar. It's a C#(?) replica of the classical-style Windows taskbar from 95 to XP eras. It even has the same icons and hides the original Windows 10 taskbar. It actually feels uncanny, running something so close to the real thing on such a new OS. It's very nice.
Other than that, I don't know of anything that would e. g. get rid of the new Control Panel or other mandatory parts. In practice, if you replace the things I listed above, it's really unlikely that you'll come across the stock Windows UI in the course of normal daily use.