Clemens Klokmose proposed a list of six properties for malleable software that I love (via Andy Matuschak)

"malleable: users can adapt tools to fit idiosyncratic preferences and uses

shareable: multiple users can work on the same data, using their own views and tools

distributed: the data and tools can be used on different kinds of devices, in different situations (desktop, tablet, phone)

composable: the user's preferred tools can be combined into workflows well adapted to their activity

interoperable: different tools can interact with the same data, so that the user can always use the "right tool for the job"

computational: the system behaves and responds dynamically"