This guy totally Pwns! Trust me
from his website
“Obviously everyone’s always wanted to write their own music for the 2600. So here it is: a sort of Atari 2600 tracker. You edit music data in a text file where patterns are created and sequenced into a song. Then you assemble the music data into an Atari 2600 ROM which will play on 2600 emulators or on a real Atari 2600 using a Supercharger or Cuttle Cart.
You can use it to write backing beats or tracks for your music, or develop music for 2600 homebrew games. The driver uses a very small amount of 2600 resources so it can easily be placed into game code. There is a growing demand for 2600 homebrew music so it would be great to have more 2600 music programmers.
I’ve recently released version 2 of the music kit with a much more advanced driver and player. Grab the latest version below.
And 2600 music programming can be a bit difficult, so I’ve written a new 2600 sound and music programmer’s guide which covers almost everything I know about 2600 sound and music and includes three useful sets of in-tune notes to help overcome the 2600’s very limited pitch. Download below.
Note that since I only have the DOS version of DASM tested and set up, currently the kit is only set up to run out of the box on PCs. However I know that it does work on Macs using the Mactari tools and it can probably be set up on Linux too.
If you are a musician and develop songs or backing tracks using the sequencer, you will be able to have an actual cartridge made of your sequences by sending the ROM image to Atariage.”
Music Kit 2.0
2600 Sound And Music Programming Guide
Old Music Kit 1.0
Mac users check this
Linux homies check this
sample track 01