Airfoil!

Stream What You Hear (SWYH) is a Windows application to broadcast the sound of your computer (ie: “what you hear”) on an UPnP/DLNA device such as TVs, amps, network receivers, game consoles, etc...

StreamToMe is an app for Windows, Mac OSX, and iOS that lets you stream music and video files (in a wide variety of formats) live from another computer.

TuneBlade - Stream audio to Airport Express, Apple TV, AirPlay compatible speakers and HiFi Receivers.

SoundWire lets you send any music or audio ("what you hear now") from your Windows or Linux PC to your Android mobile devices. Use it as:- A remote speaker or wireless headphones- A way to listen to music and movies from your computer anywhere in your house or out on your deck.- A wireless extension of live audio from your PC-based music systemThe full version of SoundWire enables unlimited Opus audio compression, can handle up to 10 connections at the same time, and has no ads or interruptions. It also has a special Pro Mode to set and display buffer latency precisely in milliseconds. SoundWire does audio mirroring. You can use any music player on your PC or laptop like Spotify, YouTube, or iTunes and stream the live sound directly to your Android device. SoundWire lets you listen to the free version of Spotify on your phone. »

This App makes your Android device a wireless speaker.

AirMyPC allows you to wirelessly AirPlay mirror your Windows PC screen and sound to your TV through 2nd/3rd AppleTV. Basically AirMyPC lets you to mirror your computer display through your AppleTV just like you do with your iPhone and iPad. With AirMyPC installed - all these wires that connect your computer to your TV are not needed anymore. Once installed, AirMyPC streams whatever you see and hear on your PC to your Apple TV - wirelessly. With AirMyPC installed, with a few mouse clicks, you can easily stream your family videos and images from your Windows computer to your big TV screen »

Acoustic Bridge gives you the power to redirect audio from one PC to the speakers of another PC. This enables you to send the sound from a PC with your music collection to any other PC on your network. You could even visit friends and redirect your PC audio output to their PC and speakers. Use the best speakers available wherever you are.

This is a Java application to use the speaker connected to other computer on the network. It transfers audio in uncompressed PCM format and uses 172 kilobyte per second bandwidth.

Share Speaker Player is an outstanding yet easy-to-use application to share speaker in LAN with high quality. It is a good way to decrease the cost of speaker in office, family, or other places especially with the world economy declining recently. In addition to decreasing cost, it is more environmental by less electric power expended and less noise made. So it also can resolve the problem that you couldn't hear clearly in office as a result of several speakers running in the meantime. Sharing songs resource and remote control are its highlight. This software makes sharing not only speaker but also songs resource possible with friends, families, colleagues, and so on. You can recommend your favorite songs to them and play these songs for them. On the other hand, you can enjoy beautiful songs played by others. Remote control is provided for this software. Users can send songs to the shared playlist, remove songs, reorder songs, and adjust the volume of sound on your computer, and so on. While this not means you can remotely change the shared playlist at your pleasure. The computer on which you want to change its playlist is entitled to acceptance or rejection any changes from other computers. As a result, others can remotely control playlists and share songs resource in your computer only with your allowance. Support all kinds of audio formats which are supported in Window Media Player. And this software can be hidden in the tray. Automatically running as the Windows starting up may be a good option for your setting up this software. Share Speaker Player runs under Windows 2003, XP and Vista. »

Soundfly uses Apple's AUNetSend and Soundflower to broadcast audio to another mac on your network.