The Symphony IDE is an open-source tool originally developed in the EU COMPASS (Comprehensive Modelling for Advanced Systems of Systems) research project. The focus is on modelling systems of systems. The IDE is based on the Overture platform.
Downloads of ready-to-run versions of the Symphony IDE are presently hosted on SourceForge; the current version is Release 0.4.0.
See The COMPASS Project pages to find Deliverable D31.4a.
All of the Symphony code is hosted on GitHub, under the @symphonytool organisation account. Everyone is welcome to grab it, fork it, and contribute.