Object Process Methodology prescribes more semantics to nodes (bubbles) and edges (lines). The project has largely been led by Dov Dori, from the Technion in Israel. I’ve seen the work at INCOSE (International Council on Systems Engineering) meetings, and have been impressed (i.e. it’s simpler than SysML, that was derived from UML). http://esml.iem.technion.ac.il/introduction-to-opm/
There is a Java-based software modelling tool available. http://esml.iem.technion.ac.il/opcat-installation/
While the research is conducted at a university, and OPCAT is licensed as GPL, I haven’t seen the project as open sourcing (i.e. sharing the source code in a public place, and welcoming contributors) in behaviour.
There seems to be a cloud version under development https://www.opcloud.tech/
In my conversations, I had mentioned that I use OPD (Object Process Diagram) conventions, i.e. boxes are object, ovals are processes. In prior uses of OPCAT (a few years back), there wasn’t a good export to SVG. Thus, I’ve been using graphical tools (e.g. Graphviz, draw.io) with aspirations to be like an OPD, but have been sloppy with the notation. (OPM Object Process Methodology draws the diagrams and writes code at the same time).
Video lectures for Object Process Methodology (Model-Based Systems Engineering) are available on Youtube .
These are associated with the professional certificate on Model-Based Systems Engineering (MBSE) on EdX, that are instructor-led. The first iterations of the course were done synchronously, and they’ve been working towards offering the content in an asynchronous way.
A diligent individual with access to the book “Model-Based Systems Engineering with OPM and SysML” and the Youtube video series should be able to figure things out when hands-on to the software.