  This article presents "John", an open-source software designed to help
collective free improvisation. It provides generated screen-scores running on
distributed, reactive web-browsers. The musicians can then concurrently edit
the scores in their own browser. John is used by ONE, a septet playing
improvised electro-acoustic music with digital musical instruments (DMI). One
of the original features of John is that its design takes care of leaving the
musician's attention as free as possible. Firstly, a quick review of the
context of screen-based scores will help situate this research in the history
of contemporary music notation. Then I will trace back how improvisation
sessions led to John's particular "notational perspective". A brief description
of the software will precede a discussion about the various aspects guiding its
design.
