I always liked DeskPins windows application, written by Elias Fotinis - very simple and intuitive, it allows you to make any 3rd party window, i.e. that of another application, top most (also known as "always-on-top"), and it will appear on top of other windows at all times, until DeskPins is closed. Below is a screenshot of how it works, self-explanatory:

Link for DeskPins direct download is provided here for your convenience (no ads, using Google Drive).

DeskPins was written in C++ and its source code recently made public (thank you, Elias).

If you look at the attached readme file, the original software is not meant to work on Windows Vista and above. However, it kept working all the way until Windows 7, but then unfortunately, stopped working on Windows 8 and higher. So I decided to write one in .NET with support for all OS (hopefully).

• Basic functionality is there, tested on Windows XP, 7, 8.1 and 10.
• Multi-monitor supported (verified dual extend configuration).
• High DPI supported (verified 100-200%).
• Select another window to be top most via CTRL+F11 (same as DeskPins).
• Make window under cursor top most via CTRL+F12 (save a drag-and-click).
• User friendly installer with upgrade support.
• Configurable keyboard shortcuts (select and pin window, pin under cursor).

• #17 On Windows 10 if each monitor is using different DPI, screen capture window takes portion of the screen. Workaround is to make sure all your monitors are using the same DPI. PinWin was initially designed to improve productivity on a single monitor, to avoid context switch. With multiple monitors, its usefulness fades.
• #26 UWP is not currently supported, the pin is placed on top of minimize button. Otherwise it works fine. To fix, requires framework upgrade to 4.6, which breaks XP compatibility. Vote for linked ticket - with enough votes I will create another repo with Windows 7+ OS support level, then it can handle UWP.

You can download PinWin via GitHub releases, where the most recent version is available (source code, binaries or installer).

I would like to thank below people and communities for making this project happen:

• StackOverflow, for this answer (special thanks to Hans Passant) and this answer (special thanks to Tergiver).
• StackOverflow, thanks to Barmak Shemirani for suggestion on How to compute total width of title bar buttons for 3rd party window on windows 10.
• Creators of Inno Setup, developer-friendly installer tool with a flat learning curve.