local is a oneshot service.
/etc/local.d/*.up
when it is started (typically during boot).
/etc/local.d/*.down
when it is stopped (typically during shutdown).
The files are executed in random order and in parallel.
An executable file /etc/local.d/echo.up
with the content
#!/bin/execlineb -P
echo "example"
would be executed and write "example" to the system log
upon starting the service local.
An executable file /etc/local.d/echo.down
with the content
#!/bin/execlineb -P
echo "example"
would be executed and write "example" to the system log
upon stopping the service local.