PinMe! is a portable free tool which makes it easy to set a window as "always on top" - to always stay in the foreground, above any others.
Launch the program and it adds an icon to your system tray. Use your PC as normal, and if you want a running program to stay above all others, right-click PinMe! and select that window from the list.
The program also has the ability to adjust window transparency. Select PinMe! Tools > Enable Window Transparency, move your mouse cursor over a window, then spin the mouse wheel to make it more or less transparent.
There's also an option to save full screen captures, windows or regions. Nothing too special here, although it does work with multimonitor setups.
There are a few other tweaks and customisations, too, yet surprisingly PinMe! squeezes all this functionality into a single tiny executable you can run anywhere.
We're unconvinced by the screen capture tool, and the transparency option is flawed (it takes over the mouse wheel so you can't use it for anything else), but PinMe! does provide a simple way to set windows as "always on top".