SuperCollider Updated +Created
domain-specific language unfortunately, but at least it's on GitHub, looks promising.
How to play scores and save them to files is discussed at: doc.sccode.org/Guides/Non-Realtime-Synthesis.html
Sample composition with custom synths + notes: sccode.org/1-5cl
leanpub.com/ScoringSound looks like a decent tutorial, it is basically the Csound FLOSS manual for SuperCollider.