- cal.diy by calcom, 50k stars. Open source scheduling app with Next.js, Prisma and PostgreSQL
- listmonk by knadh, 24k stars. Self-hosted newsletter and mailing list manager shipped as a single binary
- react-email by resend, 20k stars. Library for writing and sending emails as React components
- docker-mailserver by docker-mailserver, 20k stars. Container-based mail server with SMTP, IMAP, antispam and LDAP
- BillionMail by Billionmail, 16k stars. Self-hosted mail server with newsletter and email marketing tools
- mailinabox by mail-in-a-box, 15k stars. Scripted one-click install of a full mail server with SMTP and webmail
- inbox-zero by elie222, 13k stars. Open source AI email assistant for triaging and clearing an inbox
- Zero by Mail-0, 11k stars. Open source email client focused on privacy and safety
- check-if-email-exists by reacherhq, 10k stars. Checks whether an email address exists without sending mail, with an HTTP API
- tutanota by tutao, 8.2k stars. End-to-end encrypted email, contacts and calendar across all devices
- macro by macro-inc, 6.3k stars. Team workspace combining email, chat, docs, tasks, calls and CRM with AI memory
- mailflare by hieunc229, 6.3k stars. Email service for teams built on Cloudflare Workers
- useSend by usesend, 4.8k stars. Open source email sending platform with an SES dashboard, alternative to Resend
- freescout by freescout-help-desk, 4.7k stars. Self-hosted shared mailbox and helpdesk with AI-assisted replies
- mail by flectar, 1.9k stars. Native cross-platform mail, calendar and contacts client with low idle memory
- webmail by bulwarkmail, 1.5k stars. Web client for JMAP mail with calendar, contacts and files
- penguin-mail by c9dev, 565 stars. Native GTK4 mail and calendar client supporting Gmail, IMAP and OpenPGP
- paperweight by wslyvh, 558 stars. Scans inbox to find accounts and helps delete personal data
- Skykeep by YashwanthKamireddi, 416 stars. Native Windows and Linux clients for iCloud notes, reminders, calendar and more
- chroncal by DouglasdeMoura, 244 stars. Terminal calendar, todo and journal manager with CalDAV sync and SQLite
- rencal by t4t5, 222 stars. Desktop calendar app with CalDAV and ICS support, built for Omarchy
- posthorn by craigmccaskill, 218 stars. Self-hosted email gateway that forwards app mail to Postmark, SES, SMTP and others
- e2a by tokencanopy, 199 stars. Email API for apps and agents, hosted or self-hosted with Docker
- simplerelay by toinbox, 190 stars. Self-hosted SMTP relay with a web dashboard and sender access control
- docs by AurionMail, 73 stars. Documentation for a self-hostable, ProtonMail-style mail service
- openday by lortkipa, 33 stars. Self-hosted calendar in one Docker container that works like Google Calendar
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