Slack is a business-oriented messaging and project management platform for teams and enterprises. It has dozens of features and integration options that boost team productivity, enhance communication, and improve workflow.

However, its free version lacks many significant features as a full archive search, messages export, analytics and more.

Here, we provide you with a set of web-based open-source Slack alternatives that are also self-hosted, which means that you can download and install them on your server and have complete control over your data.

1- Mattermost

Mattermost is a free open-source self-hosted multi-user chat platform. It is written in Go and JavaScript (React). It supports 16 languages. It may not differ much from Slack, as it supports team, groups, creating multiple workspaces, attachments, and offers clients for Windows, Linux, and macOS.

Like Slack, Mattermost features hashtag support, channels, workspaces, threads, file and document attachments, and full-text search for messages.

However, as a self-hosted system that puts you in full-control of your data, and install, you can search all of your previous messages without a limit, which you can not do in Slack unless you are on the enterprise plan.

2- RocketChat

RocketChat is another Slack alternative messaging platform that you can self-host at your server. It supports audio and video calls, file attachments, full-text search, and many other features.

RocketChat offers mobile and desktop clients alongside a web version which supports mobile as well.

Like Slack, Users can create groups, use hashtags in messages, pin and bookmark messages, and allows a high level customization.

RocketChat comes with a desktop clients, web self-hosted server/ client, and mobile apps.

It supports webhooks, embedded chat widget, and features a rich real-time API.

3- Nextcloud Talk

Nextcloud is an open-source self-hosted cloud platform for teams and groups. It has a vast ecosystem that contains apps anyone can install and run. Some of these apps offers a real-time chat and messages between users system users.

The chat module or apps allows an integration with other apps and modules such as file sharing, calendar, project management and more.

Many companies, teams, and communities prefer Nextcloud for their daily workflow to share files among their team members, adding the Nextcloud Messaging App can be a save.

4- Zulip

Zulip is an open-source team collaboration tool with unique topic-based threading that combines the best of email and chat to make remote work productive and delightful. Fortune 500 companies, leading open source projects, and thousands of other organizations use Zulip every day.

Zulip is an open-source project that is released under the Apache-2.0 License.

It is an ideal solution for developer teams, game-dev communities, and companies of all size and sorts.

5- Tinode Instant Messaging Server

Tinode is an instant messaging server that you can self-host in your server. It is written in the Go programming language and released under the GPL-3.0 License.

It offers a client-side library, and clients for the web, desktop platforms, iOS and Android.

It is important to note that it is not XMPP/ Jabber server, it is more like Telegram.

6- Chatwoot

Chatwoot is an open-source, self-hosted customer engagement and messaging suite. Chatwoot lets you view and manage your customer data, communicate with them irrespective of which medium they use, and re-engage them based on their profile.

Chatwoot is an Open Source Self-hosted Customers Messaging System
Open-source customer engagement suite, an alternative to Intercom, Zendesk, Salesforce Service Cloud etc

7- Cabal

Cabal is an experimental chat and messaging platform that offers a similar client to slack.

Cabal is also a P2P decentralized platform. Its client works for Windows, Linux, and macOS.

8- Movim

Movim is a federated blogging and chat platform that acts as a web frontend for the XMPP protocol. It is released under the terms of the AGPLv3 license.

Movim offers a one-click install Chrome app, and a web app that works on all browsers including mobile ones.

9- Element

Element is an ideal alternative to Slack for anyone who value security and productivity. It is a group of apps built on top of the Matrix to offer a collaborative experience for Android, iOS, desktop and the web.

Element uses the ecosystem, it supports file attachments, voice recording, channels and workspaces, and voice/ video calls.

10- Wire

Wire is an encrypted secure messaging platform for team and groups. It is a GDPR/ CCPA compliant.

Wire comes with a built-in end-to-end (E2EE) encryption and audio/ video collaboration support.

Wire is available for desktop (Windows, Linux, macOS), Android and iOS. If you prefer a web version, Wire team got you covered with a responsive web client.

11- Relp

Relp is a free open-source self-hosted web messenger and file sharing app. It features push notification, offline-support, file transfer, and voice calls.

Relp is not a full-featured counterpart (alternative) to Slack, as it lacks many features that Slack has, however, it is a good alternative for small teams, community groups, families, and small companies.

12- Nertivia

Nertivia Desktop is a free open-source desktop client for Nertivia network, which offers a similar and free features to slack. It supports creating servers, channels (workspaces), message emojis, file attachments, and themes.

Currently, the desktop client supports only Windows platform, but it is expected to support Linux and macOS in the near future.

13- Dino

Dino is a free open-source end-to-end messenger for Linux, but it can also be built from source for Windows and macOS.

By default, it supports end-to-end encryption via OMEMO or OpenPGP, with a full decentralized protocol.

Dino may lack some features like channels, workspace creation and hashtags. However, it is an ideal solution for small teams, and personal communication.

With Dino, users can upload documents, images, media files and many other file formats. Unlike Slack, messages search is unlimited, and users can use multiple accounts and group chat.

14- Revolt

Revolt is a fairly new open source user-first chat platform. You can find links to useful resources about the project below. It offers a desktop app, web port, several libraries, and a self-hosted port with Docker.

Revolt backend is built with Rust, which explains its robust performance.

15- Threema

Threema is yet another free open-source secure messaging platform that uses WebRTC. It offers a web application, android, and iOS apps, that you can build and install.

Threema desktop is built on top of Electron.js which works for Windows, Linux, and macOS.

The project focuses on privacy and to be a GDPR-compliant. It can be self-hosted and customized to work on a local build apps.

Final thought

Slack is a great hosted platform for teams, but as it lacks many options for its free version, it is an essential to find a self-hosted open-source alternative. As we listed, the best free/ open source massagers and chat platforms, we hope that we offered with enough many options to pick up the one that fits your workflow.

If you know of any other open source free self-hosted platform, that we did not mention here, let us know.