—fUML and Alf are two OMG standards dealing with executable modeling in UML. fUML focuses on semantic aspects, while Alf focuses on syntax. Papyrus (the UML/SysML modeler of the Eclipse foundation) provides tool support for these two standards. The purpose of this article is to provide the community with feedback and lessons learned by the Papyrus team regarding their implementation and usage of these standards, with the perspective of domain-specific uses of the tool. The feedback related to fUML is intended to highlight how tool developers can leverage fUML semantics to develop user and/or domain-specific model execution environments. The feedback related to Alf focuses on key end-user functionality: the combined usage of Alf and UML, with or without profiles.