From Oracle®

Oracle® Cost Containment,
Challenging economic times call for prudent, effective cost management. IT budgets are shrinking at a time when information demands are rapidly expanding. EnterpriseDB's Postgres Plus® Advanced Server runs most applications written for Oracle, at a small fraction of the cost Oracle charges for database licenses and annual maintenance. EnterpriseDB offers Oracle cost containment solutions that fit a range of deployment configurations, all of which plug into your current infrastructure and leverage your existing DBA and application development skills.

PostgreSQL Doc - porting from Oracle PL/SQL,

Oracle 相容性開發者指南 (EnterpriseDB)

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Ora2Pg is a free tool used to migrate an Oracle database to a PostgreSQL compatible schema. It connects your
Oracle database, scan it automaticaly and extracts its structure or data, it then generates SQL scripts that you can
load into your PostgreSQL database.

Ora2Pg can be used from reverse engineering Oracle database to huge enterprise database migration or simply to replicate
some Oracle data into a PostgreSQL database. It is really easy to used and doesn't need any Oracle database knowledge than
providing the parameters needed to connect to the Oracle database.