Each row is a deliverable and each column a role. R does the work, A is the single accountable owner, C is consulted and I is informed. Exactly one A per row is what keeps accountability clear.
A row with no A means nobody owns the deliverable; a row with two means accountability is split and decisions stall. The single accountable role per row is the discipline the matrix exists to enforce.
R responsible, A accountable, C consulted, I informed. Press a cell to cycle; blank clears it.
Add activities and roles to start assigning responsibility, or load the London Grid example.
Up to eight activities and six roles; labels cap at 24 and 16 characters.