postgres takes a lot of design inspiration from Oracle, but AFAIK has never made any real attempt at being strictly compatible with it.
You might be thinking of dblink in oracle's world, and foreign data wrapper (fdw) in postgres, which at least lets you transparently interact between the two for just DQL. DDL, procedural logic, etc definitely differs.
There's also EnterpriseDB, a commercial version of PostgreSQL that has added support for the Oracle SQL dialect, including the stored proc language (pl/SQL or whatever it's called).
I don't think it speaks the Oracle wire protocol though.
No, it doesn't speak the Oracle wire protocol.
But the Oracle pl/slq (source code compatibility) from Postgres was ported to DB2 and IBM claims 100% compatibility.
