What Is Airplay?
There are two different parts of Airplay: streaming and Airplay Mirroring. Streaming is the basic Airplay functionality of sending music from your computer or iPhone to a Wi-Fi-connected speaker. Mirroring uses Airplay to display everything on your device's screen on another device, such as an Apple TV.
Airplay Streaming From iTunes on Windows
Basic Airplay audio streaming comes built into the Windows version of iTunes. Just install iTunes on your PC and connect to a Wi-Fi network, then you're ready to send music from your computer to compatible audio devices.
Stream Any Media Over Airplay on Windows
One of the features of Airplay that Apple only supports on Macs is the ability to stream content other than music to Airplay devices. You can stream media from virtually any program including ones that don't support Airplay since Airplay is embedded in the mac-OS operating system. For example, if you're running the desktop version of a streaming music app that doesn't support Airplay, you can use Airplay built into the mac-OS to send music to your wireless speakers.
This won't work for PC users because Airplay on Windows only exists as part of iTunes, not as part of the operating system. You can, however, download extra software to add this feature to Windows. There is a pair of third-party programs that can help:
Tune Blade is free to use on open source operating systems and costs just $9.99 for Windows.
Airfoil for Windows offers a free trial version, or you can pay $29 for the full version.
Airplay Mirroring on Windows With Extra Software
Airplay Mirroring lets you show whatever is on your Mac or iOS device's screen on your HDTV using the Apple TV. This is another OS-level feature that's not available as part of Windows, but you can add it with these programs:
AirMyPC lets you use Airplay to mirror to an Apple TV or Chrome cast connected to a TV. Add-on software for Windows permit you to use the mirrored screen like a virtual whiteboard.
Air Parrot enables mirroring to Apple TV and Chrome cast. It also allows you to mirror one program to the Apple TV while showing something else on your PC, which is not possible on Macs.
Air Server is a powerful tool designed for educators that allows a PC to receive video over Airplay. It comes with a free trial.
X-Mirage supports Airplay Mirroring to any Mac or PC and adds the ability to record what's on your screen as well as audio. It also lets you mirror more than one device at a time onto the same screen. Unfortunately, it is not compatible with Apple TV.
Airplay Receiver on Windows
Another Mac-only feature of Airplay is the ability for computers to receive Airplay streams from other devices. That way, Macs running recent versions of macOS can essentially function like an Apple TV. There are a few third-party programs that give your Windows PC this same ability:
Airplay Client for Windows Media Center is a free program that requires Bonjour, which is installed as part of iTunes on Windows.
LonelyScreen is a free program that supports both receiving and recording content over Airplay.
Shairport4w is an open source project available as a free download.