# Open-source alternatives to Slack

> Open-source alternatives to Slack that run locally, allow commercial use and need no paid API include Campfire (ONCE) (channels and direct messages, integrations and search and message history; MIT), Tuwunel (channels and direct messages, threaded conversations and integrations; Apache-2.0) and Jitsi Meet (voice and video huddles; Apache-2.0; runs on CPU). Mattermost and Synapse (Matrix) with Element cover all 5 Slack jobs.

Slack: Hosted workplace chat sold by subscription, with channels, direct messages, threads, huddles for voice and video, an app and bot ecosystem, and searchable message history. Pricing: See pricing page (checked 2026-10-15). Facts checked 2026-10-15.

## Projects

| Project | Jobs | Runs locally | Commercial use | Paid services | Hardware |
|---|---|---|---|---|---|
| [Rocket.Chat](https://repoquarry.dev/projects/rocket-chat) | channels-and-dms, threaded-replies, chat-integrations, message-search | Self-hosted (Docker, Podman, Kubernetes) or Rocket.Chat cloud hosting | Allowed, but Starter is capped at 50 users and Community at 100 concurrent users; vendor calls Community unsuitable for business-critical production | None required within the free caps; Commercial, Government and Defense plans remove limits and add support | Up to 500 concurrent users - Rocket.Chat 2 vCPU, 4 GiB RAM, 20 GiB disk; plus MongoDB 8.0+ (2 vCPU, 4 GiB per replica) |
| [Mattermost](https://repoquarry.dev/projects/mattermost) | channels-and-dms, threaded-replies, huddles-and-calls, chat-integrations, message-search | Self-hosted server (Docker, Linux package or tarball) or Mattermost Cloud | Yes; Team Edition (MIT binary) is advised for under 250 users, Entry has history and other limits; AGPL applies to modified builds; trademark needs approval | None required; paid subscriptions add SSO (beyond Entry), compliance, high availability, full history and support | 1 vCPU and 2 GB RAM for up to 1,000 users; 2 vCPU and 4 GB RAM for 1,000-2,000; PostgreSQL 14+ |
| [Jitsi Meet](https://repoquarry.dev/projects/jitsi-meet) | huddles-and-calls, screen-sharing | Self-hosted server (Debian/Ubuntu packages or Docker), or the free meet.jit.si service | Yes, Apache-2.0 | None required | 8 GB RAM suggested (4 GB for small meetings, 2 GB for tests); 4 dedicated cores for a basic server; 20 GB disk; 1 Gbit/s network for small use |
| [Zulip](https://repoquarry.dev/projects/zulip) | channels-and-dms, threaded-replies, chat-integrations, message-search | Self-hosted server on Ubuntu or Debian, or hosted Zulip Cloud | Yes, Apache-2.0 with no user caps on the self-hosted server | None required; the Mobile Push Notification Service needs a paid or free Community plan for organisations over 10 users | 1 CPU and 2 GB RAM with 2 GB swap for small teams; 2 CPUs and 4 GB RAM for 100+ users; 10 GB free disk |
| [Buzz](https://repoquarry.dev/projects/buzz) | channels-and-dms, threaded-replies, chat-integrations, message-search | Self-hosted relay (Docker Compose) plus desktop app; one-click Railway hosting optional | Yes, Apache-2.0 | None required for chat; AI agent features need an agent and model provider of your choice; Railway hosting optional | Not documented |
| [Fluxer](https://repoquarry.dev/projects/fluxer) | channels-and-dms, huddles-and-calls, message-search | Self-hosted with Docker or Kubernetes, or the hosted fluxer.app service | Allowed under AGPL-3.0; publish changes if you offer a modified version over a network | None required; optional Operator Pass (support perks) and Fluxer Plutonium | 2 vCPU and 8 GB RAM minimum with defaults (4 GB with low-memory overrides); 4 vCPU and 16 GB for a small active community; 20 GB disk |
| [Synapse (Matrix) with Element](https://repoquarry.dev/projects/synapse) | channels-and-dms, threaded-replies, huddles-and-calls, chat-integrations, message-search | Self-hosted homeserver (packages, Docker or ESS on Kubernetes); hosted Matrix servers also exist | Allowed under AGPL-3.0 (share changes if you offer a modified server); ESS Community is pitched at non-commercial use, ESS Pro is the paid business edition | None required; Element sells support and ESS Pro | ESS Community quick setup needs 2 CPU cores and 2 GB RAM; standalone Synapse needs at least 1 GB free RAM to join large public rooms |
| [Stoat (formerly Revolt)](https://repoquarry.dev/projects/stoat) | channels-and-dms, huddles-and-calls | Self-hosted with Docker, or the hosted stoat.chat service | Allowed under AGPL-3.0; publish changes if you run a modified version, and do not use Stoat branding for your instance | None required to self-host | At least 2 vCPU and 2 GB RAM recommended |
| [Wire](https://repoquarry.dev/projects/wire) | channels-and-dms, huddles-and-calls | Self-hosted on Kubernetes (Helm), or Wire's hosted service | Allowed under AGPL-3.0; share changes to a modified server and do not use the Wire brand | None required; Wire offers deployment support and the hosted service | Production - 3 physical servers, about 23 Ubuntu 22.04 VMs, 18 cores and 38 GB RAM per server, SSD only; supports up to 4,000 users |
| [Nextcloud Talk](https://repoquarry.dev/projects/nextcloud-talk) | channels-and-dms, huddles-and-calls, chat-integrations, screen-sharing | Self-hosted as an app on your Nextcloud server | Allowed under AGPL-3.0; publish changes if you offer a modified version over a network | None required | Nextcloud needs at least 128 MB RAM per process (512 MB recommended); Talk adds load per active participant and needs a dedicated or decent virtual server |
| [Campfire (ONCE)](https://repoquarry.dev/projects/campfire) | channels-and-dms, chat-integrations, message-search | Self-hosted single Docker container | Yes, MIT | None required | Not documented |
| [Tuwunel](https://repoquarry.dev/projects/tuwunel) | channels-and-dms, threaded-replies, chat-integrations | Self-hosted server (static binary, Docker or distro packages) | Yes, Apache-2.0 | None required | Not documented |

## Common questions

### Is there a free, open-source alternative to Slack?

Yes. Mattermost, Synapse (Matrix) with Element, Rocket.Chat, Zulip and Buzz are free to download and run on your own computer without paid API keys. Mattermost and Synapse (Matrix) with Element cover every job we list for Slack; the others cover only part of it, so check which job you need.

### Can I do channels and direct messages locally without a Slack subscription?

Yes, with Rocket.Chat (MIT), Mattermost (AGPL-3.0-only) and Zulip (Apache-2.0). Check the hardware notes and licence conditions on each page before you start.

### Can I do threaded conversations locally without a Slack subscription?

Yes, with Rocket.Chat (MIT), Mattermost (AGPL-3.0-only) and Zulip (Apache-2.0). Check the hardware notes and licence conditions on each page before you start.

### Which Slack alternatives can I use commercially?

Confirmed: Buzz, Campfire (ONCE), Jitsi Meet, Tuwunel and Zulip. With conditions: Fluxer, Mattermost, Nextcloud Talk, Rocket.Chat, Stoat (formerly Revolt), Synapse (Matrix) with Element and Wire. This is not legal advice; read each licence.

### Does any open-source project replace all of Slack?

Mattermost and Synapse (Matrix) with Element cover every job we list for Slack.

---
Source: RepoQuarry (https://repoquarry.dev/alternatives/slack). Data licence: CC BY 4.0. Quotes are from project documentation and belong to their authors.