Auphonic Leveler is a desktop (stand alone) Loudness batch processing program for Mac and PC.
There is a free online version with a limited monthly amount of audio processing avaliable.
Automation is also available. See the Auphonic Documentation

It does an excellent job, I highly recomend it!

In the author's own words:
The Auphonic Leveler is an intelligent Desktop Batch Audio File Processor which analyzes your audio and corrects level differences between speakers, between music and speech and between multiple audio files to achieve a balanced overall loudness.
It includes a True Peak Limiter, targets for common Loudness Standards (EBU R128, ATSC A/85, Podcasts, Mobile, etc.) and automatic Noise and Hum Reduction algorithms.