At pgCon we had an BoF for projects/companies that are maintaining either forks of Postgres (ie: Aurora Postgres, EDB, Greenplum, BDR), or extensions that interact heavily with internals (ie: Citus, TimescaleDB). We’d like to have a mailing list to facilitate further discussion in this area.
BDR3 is not a fork of Postgres, but it is an extension.