For years now, Slack has been the de facto standard app and service for collaboration and group communication. There are good reasons for this:Slack is consistently reliable and extremely configurable, offering numerous options to workgroups large and small.

But for some users, Slack's proprietary license is a hard pill to swallow. On top of that, Slack can get pretty pricey (even for businesses). And because Slack is a cloud-based infrastructure, it presents the same security and privacy issues as any cloud service.

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For those who prefer their software and services to be open source, fret not because options are available. Whether you're just getting a company off the ground, looking to switch from Slack, or even want to use such a service for family communication and collaboration, here are five open-source alternatives to Slack.

1. Element

Element is more about communication but it also offers file sharing, video and voice calls, and organizational features that make collaboration possible.

Unlike many collaboration tools, Element takes a decentralized approach, which means hosting happens on participating servers around the globe. This makes for a more secure option than centralized services because data is not stored in a single location. Users also have full control over their data and can ensure their conversations are safe, thanks to strong end-to-end encryption (which means only the sender and receiver can view a conversation). 

Element can be used from the web, on the desktop (Linux, MacOS, and Windows), and via your phone (Android and iOS). You can download the installable file from the official download page. 

Pricing for Element includes:

• Starter: Free for up to 200 users. Includes end-to-end encryption, instant messaging, voice calls, and admin controls.
• Business: $5/user/month. Adds fully managed cloud-based service, enhanced admin controls, and single sign-on.
• Enterprise: $10/user/month. Adds self-hosted or fully managed options, auditing & reporting, custom DNS, and group sync.
• Sovereign:  Price per deployment. Adds nationwide scalability, antivirus/content scanner, custom mobile push gateway, dedicated identity server, and branded mobile app (minimum 5k users).

2. Mattermost

Mattermost is a powerful, flexible, and secure team messaging app that can be run on your own network (for even better security) or via one of Mattermost's hosting plans. 

The locally hosted option is very appealing to many open-source users because all data is stored on a private network, therefore no third parties can access your information. At the same time, Mattermost meets compliance regulations, so you can be sure that data is secure and private.

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Features of Mattermost include access control policies (for easier user management), Active Directory/LDAP integration, automated compliance export, custom branding, multi-factor authentication, read-only announcement channels, Elasticsearch integration, single sign-on support, unlimited integrations with third-party tools, unlimited search history, guest accounts, and more.

Mattermost can be installed on Linux, MacOS, Windows, Android, and iOS.

Mattermost pricing includes the following:

• Free:Channel-based messaging for web, desktop, and mobile, 1-1 audio calls and screen sharing, operational and technical collaborations, integrations, and 20 languages.
• Professional:$10/user/month. Adds single sign-on, AD/LDAP integration, advanced access controls, group calling, guest accounts, system-wide notifications, and more.
• Enterprise:Contact for quote. Adds high availability, advanced compliance and administration, enterprise mobility, workflow automation, and more.

3. Rocket.Chat

Rocket.Chat was the G2 2024 Best Software Awards winner in Collaboration and enjoys over 12 million users in 150 countries. There are many reasons for this, such as a strong focus on privacy and data control. Rocket.Chat uses end-to-end encryption -- all messages, files, and calls are protected. 

With the self-hosted option (which is fairly easy to deploy), you gain even more control over security and data privacy. Rocket.Chat includes features like group chat, file share, voice/video calls, canned responses, customizable user permissions and notifications, guest users, multifactor authentication, audit logs, smart chat routing, unlimited message history, branding, and more.

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Rocket.Chat can be installed on Linux, MacOS, and Windows, as well as Android and iOS.

The price structure of Rocket.Chat looks like this:

• Starter:Free. Up to 25 users and up to 100 monthly active contacts, unlimited apps and push notifications, read receipts, full matrix federation, LDAP, SAML, and OAuth support.
• Pro: $4/user/month. Up to 500 users and up to 100 monthly active contacts, adds Rocket.Chat watermark removal and webform/email support.
• Enterprise:Contact for pricing. Custom users, custom monthly active contacts, custom monthly active users and microservices, multiple instance scaling, custom roles and permissions, audit panel, device management, and embedded chat experiences.

4. Wire

One thing that differentiatesWire from others is that it operates as a transparent, subscription-based service, which means your data is not seen as a product. Wire provides 100% digital sovereignty, is used by most G7 countries, and adds compliance for official communications. Wire is even used for official, confidential communications in Germany, so it does take security and privacy very seriously. 

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Wire includes the usual features for communication (such as chats and video/voice calls/conferences) and adds custom settings (such as device verification), simple onboarding, email or SSO registration, encrypted file sharing and individual encryption for one-on-one and group conversations, dedicated link invite, guest rooms, and self-destructing messages. 

Wire can be installed on Linux, MacOS, Windows, Android, and iOS.

Pricing for Wire looks like this:

Wire doesn't offer a free plan, but does include a free trial. Plans start at$5.83/user/month for teams and go up to$9.50/user/month for enterprise businesses.

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Any one of these services would be a viable alternative for Slack. If you'd rather be using open-source software that is more flexible and secure, I would highly recommend you give one of these options a try. For even more data security and privacy -- if you have the ability -- start out with one of the above services that allow you to self-host.

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