Modeling Human Computer Interaction (HCI) is nowadays practiced by IT companies. However, it remains a straightforward task that requires some advanced User Interface (UI) modeling tools to ease the design of large-scale models. This includes tackling massive UI models, multiplicity of models, multiplicity of stakeholders and collaborative editing. This paper presents a UI multimodel editor for HCI, illustrated on task modeling. We present innovative key features (genericity, creativity, model conformity, reusability, etc.) to facilitate UI model design and to ease interaction.