This paper presents an adaptive and adaptable system and its evaluation. The system is based on a commercial spreadsheet application and provides adaptation opportunities for defining a user- and task-specific user interface (new menu entries and key shortcuts for subrouting names and parameters, changing default parameters). The development following a design-evaluation-redesign approach has shown that adaptations are accepted if the user has the opportunity to control their timing and content. This does not necessarily mean that the adaptation is initiated and performed by the user alone (adaptability). On the contrary, the strictly user-controlled adaptation is too demanding for the user. The paper shows how the user's own adaptations can be supported by the system by initial adaptive suggestions showing the rationale of adaptations and the way to perform them.