Squeezebox is a line of networked audio and control components. Most of them play streaming audio from your favorite source. Most of them are able to display graphical output of various quality. Some of them are designed to control the audio players. All the communication between all components is through WiFi or standard LAN cable. All the components are connected to your home LAN as if they were standard computers (i.e. they have they normal IP addresses and hostnames, you can log into them and hack them, etc.). Any of your home computers can function as both "player" and "controller" of any other component (yes, including command line scripting).
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First of all, these components "just work" out of the box. For example, you just connect the player to any WiFi network with access to the Internet, it automatically updates its firmware and is immediately able to play any streaming audio from the Internet. That's all. You don't have to install anything anywhere. In fact, you can just connect it to some public WiFi network and don't even have to own any computer.
However, it gets much more interesting when you have your own MP3 collection and a home computer which is running all the time. You install Squeezebox Server on this computer (it supports Windows, Mac and Linux) and then you can play anything from your music collection on any of your Squeezebox players or on any computer connected to your home network. Of course you can play different albums on different devices and everything can be controlled either via Squeezebox remote or via browser interface from any of your home computers:
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Squeezebox doesn't force you into any proprietary solutions and does not lock you in. Your music collections is simply a collection of folders and subfolders containing audio files and cover art images. Everything is indexed according to standard ID3 tags and Squeezebox's private database and indexes don't clutter your music folders - they are kept completely separate.
I now have Squeezebox Player (just a miniature box connected to external speakers), Squeezebox Remote (WiFi remote control with full color display) and Squeezebox Boom (audio system with built-in speakers and large monochromatic display).
Audio quality obviously depends on what kind of Squeezebox device you are using (the most expensive system costs 10x more than the cheapest one) but my mid-range Boom has perfectly clear sound and is totally quiet when not playing.
I know there are many similar soultions but I have never experienced anything that simply works as effortlessly as the Squeezebox. There are lots of thoughtful touches, for example the way the alarms and display dimming work and can be configured so that the device does not disturb you when you sleep and you can be awakened by your favorite song or your favorite radio station.
On the other hand, Squeezebox is a godsend for all control freaks because the configuration possibilities are staggering and all the software (including the server and firmware in all devices) can be fully customized - the server itself is written in Perl and the devices are running Linux. However, I didn't have to do that - I am perfectly happy with the standard configuration options and I don't even use all of them: For example, your Squeezebox device can display your Flickr photos, your RSS feeds, you can play games on it etc...
I really love tech gadgets and I must stress again that there are not many gadgets that I found as useful and as capable as the Squeezebox family of products.