Yay, a new tool for making music on the Atari VCS/2600! Slocum Tracker is essentially a web-based graphical front-end for Paul Slocum's "Music Kit 2.0". Slocum Tracker doesn't feature any sound (yet?), so you still need to compile'n'run the binary to check the result. But it's obviously still an improvement over having to hard-code the music in asm.
The project is open source, source code is available on the author's github.