Open Network Computing, a set of network protocols originally created by Sun Microsystems.
The base layer is an implementation of Remote Procedure Calls (ONC/RPC). Data sent over RPC is encoded in the host-independent External Data Representation (XDR). A number of services are built on top of these layers, most notably NFS (a Network Filesystem) and NIS (Network Information Services).
Current responsibilty for designing the next generation of ONC lies in the hands of an IETF working group. The various ONC protocols have been defined in these RFC's: