Mailtrain - Self-hosted open-source Mailchimp clone
Hacker Newsletter - Best of Hacker News in your inbox every Friday.
Listmonk - Send e-mail campaigns from a powerful dashboard. High performance and features packed into one app.
Why is this interesting? - Every weekday Noah Brier & Colin Nagy (and friends) send an email about something interesting.
Kill the Newsletter! - Convert newsletters into RSS feeds
Consoom - Easily subscribe to and read your favourite newsletters.