DarkWave Studio is a free and open source digital audio workstation.
The program is a highly professional music creator that includes a virtual studio, pattern editor, sequence editor and multitrack hard disk recorder.
You get a stack of plug-ins, too. There's MIDI input and output, an 8-track stereo mixer, a couple of drum synths, an oversampling filter, echo and reverb effects, and more. And support for VST/VSTi instrument and effect plugins means you can expand DarkWave Studio to do just about anything you might want.
Some elements of the program are quite easy to use. The virtual studio allows you to connect machines as you'd like, for example, and working in the pattern editor is just a matter of clicking to add or delete notes, or dragging to resize them.
Elsewhere, though, there's very little documentation and the developer assumes that users know exactly what they're doing. If you're a music-making novice then DarkWave Studio probably isn't for you.
Version 5.7.1 brings (full changelog):
While complex and short on documentation, DarkWave Studio is a very capable music creator, recorder and production tool, well worth a look if you've the time to invest in learning how it works