(OPF) Any system for storing objects so they can be reloaded into a future session. Typically this will use a relational database along with some kind of object relational mapping. Another typical solution would store objects in XML files (a form of serialisation). One of the trickier problems to solve is how to maintain references between objects, e.g. replacing memory pointers with unique names or identifiers.
Virtually identical considerations apply to transferring objects, or indeed any kind of data structure, from one process to another via some communications channel, e.g. a TCP/IP connection.
Apple's Enterprise Objects Framework (EOF) is a mature and powerful example.