Windows Vista and later versions have a built-in screenshot app called the Snipping Tool. For users who require more advanced software, Lightshot, Shotty, and the free-usage options for Screenpresso or Gyazo are good alternatives.
The Windows Snipping Tool can take full-screen or resizable screenshots and capture specific windows. The tool also provides a delayed screenshot setting and is suitable for most basic use.
Screenpresso is designed for users who want to set hot keys or create animated screen captures. It also provides Windows system-tray integration and a gallery for viewing screenshots.
Gyazo simplifies sharing screenshots online and is available for Windows, Mac and Linux.