What "open source" means and where Slack stands
Open-source software is distributed with its source code under a licence that allows anyone to read, modify, and redistribute it. Slack does not meet that definition. The desktop application, the mobile apps, and the backend infrastructure are all closed and proprietary. Salesforce, which acquired Slack in 2021, controls every aspect of the codebase, the servers, and the protocol. Users cannot inspect what the application does on their machine, cannot patch it, and cannot run their own server.
This is a deliberate business decision, not an oversight. Slack's revenue depends on subscription tiers, and the product is tightly coupled to Slack's own cloud infrastructure. There is no self-hosted community edition and no published API specification that would allow a fully independent implementation.
What Slack does release publicly
Slack does offer a public API and a set of developer tools (the Bolt SDK, Block Kit, Webhooks, and the Slack App Directory). These let third-party developers build bots and integrations on top of Slack, but they are not the same thing as open-sourcing the product itself. The API surface is also deliberately limited: core messaging transport, workspace administration internals, and the voice/video layer are not exposed.
Some auxiliary tooling around the Slack developer ecosystem is released under open licences, but the client and the platform remain closed. It is worth being precise here — releasing SDKs under an open licence is a common and useful practice, and it is not the same as the product itself being open source.
Why it matters: proprietary code, Electron, and resource use
For most users, whether software is open source is an abstract concern. But with Slack it has a direct, daily consequence: the official desktop client is built on Electron, a framework that bundles a full Chromium browser engine with every application. The result is an application that can consume well over a gigabyte of RAM during a normal work session, takes several seconds to start, and keeps CPU cores busy even when the window is idle in the background.
Because the code is proprietary, users have no recourse. You cannot recompile the client with a lighter rendering engine, you cannot disable the features you do not use, and you cannot audit what the application is sending over the network. You accept the binary as shipped.
This is a structural limitation of the closed-source model, not a criticism of any individual engineer. The same constraint would apply to any proprietary Electron application.
msga: a GPL-3.0 open-source Slack client
msga (Make Slack Great Again) is a free, open-source desktop client for Slack built in C++ and Qt6 — the same framework used by Telegram Desktop. Because it is a native application rather than a web wrapper, it starts in under a second, idles near 0% CPU, and uses a fraction of the memory that the official Electron client requires — roughly 60–100 MB under typical use.
The full source code is published on GitHub under the GPL-3.0 licence. Anyone can read it, audit it, report issues, or contribute patches. It works with the Slack workspaces you already belong to — there is no separate account or service.
msga runs on Linux, macOS, and Windows, and it is the only native, open-source Slack client built on a modern C++/Qt6 stack. It is honest about its current state: some Slack features are still on the roadmap, and the project is under active development. If you rely on every Slack capability, it is worth checking the project page before switching entirely. But for the core use case — reading and writing messages across your workspaces without a browser engine running in the background — it works today.
Why GPL-3.0 specifically
The GPL-3.0 licence is a strong copyleft licence. It guarantees that anyone who distributes a modified version of msga must also release the source code of their modifications under the same terms. This is a deliberate choice: it prevents a scenario where a company takes the work, adds proprietary changes, and ships a closed binary. The community's contributions stay in the commons.
For users, the practical meaning is simple: you can always obtain the source, build the application yourself, and verify that it does what it claims to do. That is a meaningful property for software that handles your work communications.
Summary
| Slack (official) | msga | |
|---|---|---|
| Licence | Proprietary | GPL-3.0 |
| Source available | No | Yes |
| Client technology | Electron (Chromium) | C++ / Qt6 (native) |
| Approximate RAM use | 1–2 GB+ | ~60–100 MB |
| Self-hostable backend | No | Uses Slack's API |
| Platforms | Linux, macOS, Windows | Linux, macOS, Windows |
Slack is a useful product, and for many teams it is the right choice regardless of its closed-source nature. But if the question "is Slack open source?" matters to you — because you care about auditability, resource use, or software freedom — the honest answer is no, and msga exists precisely to offer an alternative path. You keep your Slack workspaces; you replace the heavy, opaque client with something lighter and transparent.
If that sounds worth trying, you can download msga or browse the source on GitHub.