Variability modeling is at the heart of product line engineering. Variability models entail features and architectural elements, technical customization aspects, sales and marketing decisions, as well as complex traceability information. In this paper we describe DecisionKing, a variability modeling tool that offers a great degree of flexibility and extensibility and allows the creation of variability modeling tools for different domains and organizations. The tool is part of the DOPLER approach (Decision-Oriented Product Line Engineering for Effective Reuse) developed in an industrial research cooperation with Siemens VAI. We report on ongoing tool development and present experiences of using DecisionKing.