Sirius Web: 100% open source cloud modeling platform
Sirius is a field-proven technology and a popular Eclipse project created in 2013, used by hundreds of developers and organizations around the world to create domain specific modelers (see the Sirius Gallery for public examples of what has been built with it). If you have to create a graphical modeling workbench for your own DSL, then you know how powerful Sirius is to help you design your own designer based on EMF.