Ardour is a professional multichannel hard disk recorder being developed by Paul Barton-Davis and is licensed under the GPL. It is written in C++ and uses GTK--. It requires ALSA, and is designed mainly for use with professional soundcards, although it will work with cheesy soundcards also.
It is capable of simultaneously recording 24 or more channels of 32-bit audio at 48kHz, and is designed to replace hardware HDR systems. It is currently in heavy development, so it's not easy to get running if you're not familiar with CVS and other programming tools. In the not that distant future though, it should be quite stable and definitely very useful for recording artists using free software everywhere.