pgnotifyd connects to a PostgreSQL database, listening for the named asynchronous notification. When notification is received, it executes the given command. It can work as a drop-in replacement for polling a PostgreSQL database for changes (eg. using crontab(5)) and is typically a cleaner and more efficient alternative.
Instructions are in the man page provided with the source code.
The current release is pgnotifyd-0.4 (27th October 2017)
There is a Git repository:
git clone http://www.pogo.org.uk/~mark/pgnotifyd.git
Source code is distributed under a BSD license