Variability modelling with feature models is one key technique for specifying the problem space of Software Product Lines (SPLs). To allow for the automatic derivation of a concrete product based on a given variant configuration, a mapping between features in the problem space and their realisations in the solution space is required. It is crucial to support the developer in the complex task of defining such mappings. These mappings can also be used to provide visualisations of the variant space that allow to reason over variability in SPLs. In this paper we present FeatureMapper, a tool that allows for defining mappings of features to model elements specifying feature realisations. These feature realisations can be defined in arbitrary Ecore-based languages. Furthermore, the tool supports different visualisation techniques that can help developers understand the complex designs of SPLs. Categories and Subject Descriptors D.2.2 [Design Tools and Techniques]: Computer-aided software en...