Try Irfanview. It's free for personal use. If it is running Press C or use menu bar -> options -> Capture/Screenshot... for screenshots.
There are many different ways to choose captured area like full desktop, foreground window or fixed screen.
You choose custom hotkey or timed screenshots. You can use a dedicated folder or your last used printer.
If you are an advanced user, you can use its command line options to write a script.
There are many different applications for Linux like GIMP or built-in in every Linux desktop environment. Just press printscreen for a screenshot.