Curated open-source alternatives to the software you already use.
Open-source threaded team chat designed to keep team communication organized and productive.
ReplacesSlack
WupNext is a self-hosted to-do and task queue app: groups, subtasks, deadlines, a built-in pomodoro timer, email reminders, and an MCP server so an AI client can work the board. Server-rendered Django with HTMX, backed by SQLite.
ReplacesTodoist
Modern, open-source WhatsApp Business Platform with real-time chat, chatbot automation, bulk campaigns, template management, and voice calling via Meta's Cloud API.
ReplacesSlack
Open source alternative to Resend, Sendgrid, Postmark etc.
ReplacesMailchimp
High performance Matrix homeserver written in Rust. Official successor to conduwuit - a scalable, low-cost, enterprise-ready alternative to Synapse.
ReplacesSynapse
Synapse is the reference homeserver implementation for Matrix, an open standard for secure, decentralised, real-time communication.
Open SourceCommunication
Stalwart Mail Server is an open-source mail server solution with JMAP, IMAP4, POP3, and SMTP support and a wide range of modern features. It is written in Rust and designed to be secure, fast, robust and scalable.
Open SourceCommunication
Soketi is your simple, fast, and resilient open-source WebSockets server.
ReplacesSlack
Open-source, self-hosted email marketing platform with BYO SMTP. Manage subscribers, templates, broadcasts, and scheduled campaigns from one place.
Open SourceCommunication
Free and open source webmail software for the masses, written in PHP.
ReplacesGmail
Rocket.Chat is a free and open-source web chat platform that allows you to build and manage your own chat applications.
ReplacesSlack
Open-source email platform for transactional mail, campaigns and inbound, with its own KumoMTA delivery and spam filtering.
Open SourceCommunication
Complete mail server solution with SMTP, IMAP, POP3, antispam, antivirus, web administration and webmail client.
Open SourceCommunication
Plunk is the open-source, affordable email platform that brings together marketing, transactional and broadcast emails into one single, complete solution
Open SourceCommunication
Open-source notification infrastructure for multi-channel workflows — in-app Inbox, email, SMS, push, and chat — with a unified API and dashboard.
ReplacesSlack
Open-source newsletter and notification platform that empowers teams to create, send, and track communications at scale.
ReplacesSlack
Nebulynk is a self-hosted collaboration platform for teams with real-time messaging, file sharing, video meetings, and AI-powered transcription and summaries.
ReplacesSlack
Mumble is an open-source, low-latency, high-quality voice chat software primarily intended for use while gaming.
ReplacesSlack
A single point of collaboration. Designed specifically for digital operations.
ReplacesSlack
Full-featured open-source mail server as a set of Docker containers: SMTP (Postfix), IMAP (Dovecot), Rspamd antispam, admin UI with DKIM management and Roundcube webmail.
Open SourceCommunication
Mailpit is a tiny, self-contained, and secure email & SMTP testing tool with API for developers.
Open SourceCommunication
MailCatcher NG runs a super simple SMTP server which catches any message sent to it to display in a web interface. Point your app's SMTP settings at mailcatcher-ng:1025 and inspect every captured email in the browser.
Open SourceCommunication
Lobe Chat - an open-source, modern-design AI chat framework.
ReplacesSlack
LiveKit is an open source platform for developers building realtime media applications.
ReplacesTwilio
Showing 24 of 40 apps
Stars from GitHub · Oct 5, 2026. Comparisons describe overlapping use cases, not feature parity.
