Zulip

Zulip is a powerful, open source group chat application. Zulip provides the benefits of real-time chat, while also supporting asynchronous communication. Zulip is inspired by email’s threading model: every channel message has a topic, just like every email has a subject.

Commerical Alternatives

Slack

Features

Markdown optimized for chat
Inline image, video and tweet previews
Code blocks
Customizable automatic linkification
Keyboard shortcuts
Enterprise grade security

Pricing

Zulip plans vary from $0/user/month to $6.67/user/month for the cloud version, and pricing for the on-prem version is custom.

Self hostable

Yes

Customers

Akamai, Wikimedia, MariaDB, LevelUp

Reviews (Snippets from G2)

Pros

Zulip is an excellent platform to have a good quick chat platform that I can join or create many channels for each team or group that I associate with.
Zulip is really an excellent platform for developing a space for workplace chatter. It is easy to switch between different channels and private chats.
Another feature that quite useful in Zulip is they provide a keyboard shortcut that can make your communication easier, like making a new topic or to write a email.

Cons

It can become clustered when there are multiple people on one conversation and it does not integrate with other organizational software well.
User Interface is tedious and navigation is a bid of pain.
The File sharing interface also seems a little bit awkward and needs some getting used to.
What I dislike about Zulip is the notification is a little bit buggy as sometimes I don't get a notification when someone mention me in public stream channel.

Github Activity

View Github Readme

Similar open source alternatives

Mattermost

Business communication

Slack

Mattermost is an open source, self-hosted, private cloud messaging solution compared to Slack which does not have the option to self-host. Security concerns still remain the number one barrier to a cloud computing deployment. With Mattermost, compliance is easy as the data does not leave the customer's premises. It’s perfect for businesses that want to keep their messaging app under tight control. Slack offers 2000+ integrations which covers all applications businesses use. While Mattermost has 100s of integrations as well, the use-case coverage is still limited when compared to Slack.

Rocket.chat

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Rocket.Chat varies from Slack by not having anything similar to Slack Workspaces. It has channels, private channels, direct messaging and even OTR (Off-the-Record) chats. In an OTR session with another user, all messages will be end-to-end encrypted and will be deleted after the session. Like other open source alternatives to Slack, Rocket.chat also loses out on some customers because of the lack of integrations with the rest of the business ecosystem.

Element

Business communication

Slack

Element is an open-source instant messaging client. Element supports end-to-end encryption, groups and sharing of files between users. With Element, conversations are hosted and owned entirely by the participating servers, instead of being stored centrally somewhere in the US, which is particularly attractive to European governments and military.