The documentation for the RTOp package is broken up into the following three separate doxygen documentation collections:
Fundamental Vector Reduction/Transformation Operator Interfaces: This minimal amount of code defines the basic interoperability mechanism for RTOp.
Support Software for Vector Reduction/Transformation Operators: This software makes it easier to provide concrete RTOp implementations and to perform global reduction operations using MPI.
Collection of Concrete Vector Reduction/Transformation Operator Implementations: This is a collection of concrete reduction and/or transformation operators.
You can browse all of RTOp as a single doxygen collection. Warning, this is not the recommended way to learn about RTOp software. However, this is a good way to browse the directory structure of rtop, to locate files, etc.