OK, there have been questions and I haven't see enough answers, so I hunted down a few!
The "Actual Technologies Adapter" referenced in:
What external SQL data sources are certified for FileMaker 15?
MS SQL Server 2008 R2
MS SQL Server 2012
MS SQL Server 2012 SP1
MySQL 5.6 Community Edition (free)
Oracle 12c R1
Oracle 11g R2
IBM i 7.1 (AS/400) (via Actual Technologies Adapter)
IBM DB2 10.5 (via Actual Technologies Adapter)
PostgreSQL 9.4.4 (via Actual Technologies Adapter)
... lead me to the Actual site:
While primarily Actual Tech has filled in the Mac user's drivers to SQL (& others), this new one, Actual ESS Adapter says:
The Actual ESS Adapter lets you use Postgres and DB2 databases with the "External SQL Sources" (ESS) feature of FileMaker 15. The adapter is available on Mac OS X and Windows. On OS X, it works in conjunction with the Actual Open Source Databases driver to connect to Postgres. On Windows, it integrates with native ODBC drivers for Postgres and IBM DB2.
read that again: OS X and Windows (but read the entire parag. carefully!)