This paper provides a discussion of how the electronic, solely ITbased composition and performance of electronic music can besupported in realtime with a collaborative application on a tabletopinterface, mediating between single-user style music compositiontools and co-located collaborative music improvisation. After having elaborated on the theoretical backgrounds of prerequisites ofco-located collaborative tabletop applications as well as the common paradigms in music composition/notation, we will review related work on novel IT approaches to music composition and improvisation. Subsequently, we will present our prototypical implementation and the results.