http://en.wikipedia.org/wiki/Tracker_(music_software)
I have yet to find a faster way from idea to music. It's clunky to get into until you spend some time to learn the idea and build up a collection of music and wrap your brain around the entire concept, but it's a few decades old a very mature concept with tens of thousands of works created with this method.
Here's a site that streams tracked music 24-7 http://www.scenemusic.net/demovibes/
Some of it is quite good (thought the quality obviously ranges quite a bit though both talent and technology).
If you want to see the music with a visual production try http://demoscene.tv/
I've been working with a piece of software called MadTracker 2 for a while, but I'm about to transition to Renoise (MadTracker 2 is long since a dead project) which is available for Windows, OS X and Linux and is about as professional as a piece of software has any right being.
In a rush I can crank a reasonable tune out in a few hours. I've heard of at least one major artist cranking out an entire album (vocals and all) in less than a week.
Most of the modern trackers will let you render individual tracks to file for final downmixing.
Note: These are most definitely not intended for live performance, though a few folks have used them for that purpose.