Portable Distributed Objects (PDO) is an application programming interface (API) for creating object-oriented code that can be executed remotely on a network of computers.
It was characterized by its very light weight and high speed in comparison to similar systems such as CORBA.
PDO, on the other hand, relied on a small number of features in the Objective-C runtime to handle both portability as well as distribution.
The PDO object then forwarded the invocation to the remote computer for processing and unbundled the results when they were returned.
This was a price most were unwilling to pay, as at the time C++ was more widely used and the effort to shift codebases to an entirely new language and paradigm was considered too onerous.