At a prior company we just wrote our own custom workflow engine which was basically a DAG processor where each node called some code. Of course, the code calle

At a prior company we just wrote our own custom workflow engine which was basically a DAG processor where each node called some code. Of course, the code called could modify the DAG in place and accomplish exactly what you're describing. It worked quite well but we didn't polish it as much as we could have. I've been wanting to do a clean-room reimplementation as of late just because I miss certain things about it.