http://www.hydrogenaudio.org/forums/...opic=65497&hl=

Since 20th August, the open source multimedia framework FFmpeg has support for the Apple Lossless format in the form of a native encoder for the very popular, cross platform libavcodec. The encoder provides compression comparable to iTunes and files are also known to work on the iPod.

You can check it out by grabbing a recent Subversion checkout from :
http://ffmpeg.mplayerhq.hu/download.html

News item based on : http://ffmpeg.mplayerhq.hu/index.html

EDIT : Comparison Chart between various ALAC encoders