Newsletter Guide - A 201 guide for taking your newsletters to the next level
Podtribe - Join and create podcast communities
Newsletters by Refind - The easiest way to email a link digest to your fans
Shuffle for Podcasters - Connecting to your podcast fans just got a lot easier.
Newsletter Crew - Podcast, blog, and community for newsletter creators.
Spectrum - Browser-based app to visualize the frequencies of an audio file.