This is a device with a user interface allowing you to select music sources (servers), to browse their content and select songs to play.
The source could be internet radio stations or your own music collection
on a server in your home network.
As these players use internet technology to access the source, you need a
home network.
To access a music server, it must talk the same protocol.
In general UPnP AV is used. If not, you are locked into a proprietary protocol.
The player must support the audio formats on the server or the server supports conversion on the fly (transcoding).
The player converts the audio stream to analogue. Digital out might also be supported.
You can connect it to an amplifier.
Some have a build in amplifier. You must supply the speakers.
Players with build in speakers are called internet radio.
Wireless digital internet radio and MP3 player
• Plays internet radio without the use of a computer
• Streams MP3 music from your computer or network
• Supports over 10.000 radio stations, including BBC 1,2,3,4 and 5Live
• Supports MP3, WAV & WMA
• Alarm clock functionality
• Live RSS feeds / Blog feeds in display
• Built-in speaker and WLAN antenna
• Stereo audio out (2 x cinch) to connect to amplifier set
• Line out (mini jack ) to connect to headphones or active
speakers


Linn’s first attempt at streaming audio players was the Klimax DS
Today they have a range of UPnP players:
| Klimax DS Player | $18,500. |
| Akurate DS Player | $6,850. |
| Majik DS Player | $3,500. |
| Sneaky Music DS Player | $2,000. |
Network: ethernet
Protocol: UPnP™ AV 2.0
Formats: up to 24-bit/192 kHz native sample rate, FLAC, WAV, MP3 & AIFF
Analogue audio outputs: RCA / XLR
OS: RTEMS
Open source: http://oss.linn.co.uk/


Network: ethernet/Wlan (WEP/WPA)
Protocol: DLNA/UPnP
Output: 1x analog (RCA), 1x optical Toslink, 1x S/PDIF coaxial cinch
Audio format: WAV, FLAC, MP3 (128 to 320 bit/s)/ Internet radio
4.3" wide-aspect ratio, colour touch-screen(480 x 272 pixels)

100 Watt amp
Protocol: UPnP/Internet radio/file sharing
Network: Ethernet/Wifi


Also available with build in amplifier.
Network: ethernet/Wlan. First unit must be connected to router using a cable or you use a ZoneBridge for an all wireless setup.
Number of tracks limited to 65.000
Protocol: CIFS / SMB (file sharing) to access NAS/PC/Mac
Output: Analog (RCA) and digital out (Toslink/coax)
Audio format: MP3, WMA (WMA Lossless and WMA Pro are not supported), AAC (MPEG4), Ogg Vorbis, Audible (Format 4), Apple Lossless, Flac, WAV, AIFF
Resolution: 16 bit / 48 kHz
Internet radio: RadioTimes, MP3 and WMA streaming audio formats

One of the first streaming audio players by Slimdevices.
Looks like Logitech stopped producing them but it is a classic indeed.
Squeezeboxes use their own proprietary protocol.
You need an computer in your home network running SlimServer/SqueezeCenter/Squeezebox Server /Squeezebox Server or what ever new name Logitech marketing department conjectured up to access your own music collection.
Often a NAS is used like the Vortex box


High end version of the SqueezeBox.
Protocol: proprietary streaming protocol, requires SqueezeCenter software to play your own music.

Network: ethernet/Wlan
Protocol: DLNA/UPnP
Output: Line out, headphones out, S/PDIF digital optical out 44.1/48 kHz
Audio format: MP3, OGG, WMA, WAV / Internet radio
Touchscreen 3.5" colour LC display for function and track information
(ID3 tags, album cover, file name etc.)
Network: ethernet/Wlan
Protocol: UPnP
Formats: MP3, WMA, LPCM, WAV, FLAC, AAC, OGG-Vorbis
A box having both digital and analogue inputs sending the audio over ethernet or WiFi to powered speakers.


THIEL SCS4 powered speaker with WiFi and ethernet inputs only!

The zöet was announced in 2008 but as far as I know not on sale yet.
A partnership between THIEL en Olive was announced early 2010.