Ardour is a free audio workstation for Linux and the Mac. Primarily the creation of Paul Davis, it is quite simply one of the most powerful audio software around. It has a whole bunch of features such as unlimited buses and audio racks, MDI CC control, precision algorithms for EQ and more. In fact its recording capability is only limited by your hardware.
If you use it to record on exiting material the program can perform latency compensation and it can monitor using hardware, and this feature allows you to apply plugins to Ardour and see the effects in real time. Its anything to anywhere routing allows for support of unlimited track, and you can also automate panning as well as plugin parameters.
Adour also has extensive editing capabilities such as time stretching, splitting and dragging, and it also comes with a beat detector and cross fade editor. There are no limits to its redo/undo, and you can use it for audio mastering too.
Furthermore, Ardour conforms to industry standards so there will be no compatibility problems when you run it. You can also import or export entire sessions or just parts of it, as it has a database manager built in. Other notable features include MIDI level machine control, no copy-protection and 32 bit floating point for the audio path.
This is just an overview of the things that you can do on Ardour. If youíre looking for a free powerful audio editor this is the one to get. It is powerful and as far as learning curves go it isnít that steep either.