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listmonk is a free, open-source, self-hosted manager for newsletters and one-way mailing lists, released under the AGPLv3 license.
Free planOpen sourceWebAPILinux
phpList is for sending newsletters, marketing campaigns, announcements and notifications, from a few hundred recipients to very large audiences. Its web interface supports personalized plain-text and HTML email, while lists, segmentation and target selection help direct campaigns. It also includes automation, A/B testing, consent tools, scheduling and campaign tracking. The free self-hosted application can suit groups that want control over their setup, though running it…
listmonk is a free, open-source, self-hosted manager for newsletters and one-way mailing lists, released under the AGPLv3 license.

SourceHut is a suite of open source development tools offered as a hosted service or for self-hosting.