Manolito,
Further to your suggestions for file explorer on Win7/10, got me a few here that you may like to try.
Code:
Q-Dir (Quad Explorer):- https://www.softwareok.com/?seite=Freeware/Q-Dir
Tiny size.
Freeware, No source code.
Very Active Development (Dec 2018).
W98 -> Win 10, x86,x64. (install or portable)
Nice Quad window explorer (changeable number and layout at push of button).
Very Good I love it.
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Double Commander:- https://doublecmd.sourceforge.io/
Open Source, very active development (Object Pascal).
Cross Platform, Install and Portable, x86,x64.
Compatible to Total Commander plugins. Double Commander Plugins available(some with source):- https://github.com/doublecmd/doublecmd/wiki/Plugins
Dont like default fonts, but easily changeable.
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Multi Commander(updated Aug 2018):- http://multicommander.com/
Free Personal, Commercial, Government. Optional donation.
About 7MB,.
Duel panel.
Win XP -> W10, x86 & x64, Install & Portable.
Extensible via scripting/automation and plugins, SDK availble (no source code).
Active Forum.
Seems very good.
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Explorer++:- https://explorerplusplus.com/download
No longer supported (source code available, cpp).
Windows x86,x64 Portable only.
Pretty good single pane.
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Windows File Manager (WinFile)
The Windows File manager was originally released with Windows 3.0 in the early 1990s.
You can read more about the history at https://en.wikipedia.org/wiki/File_Manager_(Windows).
WinFile on GitHub:- https://github.com/Microsoft/winfile
Binary:- https://github.com/Microsoft/winfile/releases
Open Sourced by MicroSoft(April 2018) (Updated for Win10/10.1, June 2018).
Changed from original source to compile in recent Visual Studio and run on recent Windows.
Windows W98->W10, Portable, x86,x64.
Requires VS CPP 2017 Runtimes.
Basic and portable, familiar to many.
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6 Best Free File Managers Alternatives To File Explorer:- https://fossbytes.com/best-free-file-managers-windows-10-alternatives/
26 best file managers for Windows:- https://www.slant.co/topics/2404/~best-file-managers-for-windows
I love the Q-Dir one, and both Commander's could well be useful.
EDIT: Above the ones I liked out of about 10 of the best.