Probably, the reason behind is to promote some of its products while offering a process compression that reduces the size of audio files to 406-% without loss of information and quality.
An addition to the project is called the alacconvert, a command line utility which can read and write audio data to and from Core Audio Format, as well as Wave files. Expect ALAC to be available on nearly everything under the sun pretty soon.
To give you some ideas about codec and open source, Wikipedia has this information:
A codec is a device or computer program capable of encoding and/or decoding a digital data stream or signal or simply a program (an implementation) which can read or write such files.
The term open source describes practices in production and development that promote access to the end product’s source materials.
For more information, visit the Apple Lossless Audio Codec project page on Mac OS forge
Image Source from Engadget