Listmonk is great and easy to self-host on Heroku or other platforms. It offers analytics, lots of customization, scheduled newsletters list management, click tracking, templating, the ability to add your own SMTP, unstyled HTML subscriptions forms to embed on your site, etc. From what I understand, it's also GDPR-compliant.
If you're looking for a more affordable option to Mailchimp and don't mind doing a bit of setup work, it's definitely worth it!
New features are being added constantly, and the dev is very responsive and helpful.