When comparing Flock vs Zulip, the Slant community recommends Zulip for most people. In the question“What are the best on-site Slack alternatives?” Zulip is ranked 2nd while Flock is ranked 5th. The most important reason people chose Zulip is:
Instead of rooms or channels Zulip is built around topics. This allows you to have multiple conversations at the same time without conversations interfering with each another. It also allows you to reference conversations without clutter.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Cross-platform
They have apps for Windows, Mac, Chrome, iOS, Android and web interface. And all the chat sessions are always on sync.
Pro Clean and clutter free interface
Pro Cheaper than Slack
It is half the price of Slack and full of nice features like polls, assign to do's, etc.
Pro Very powerful integration APIs
Unlike its rivals, it not only allows you to receive events, but also allows you to push content to it and receive various user action events.
Pro No IT team required for setup
Moving a team or organization to flock does not require any setup from the company's IT team. At max, what might be required would be to whitelist their domain in case the organization's IT team has gotten external domains blocked. You can simply download Flock and invite others in your organization by using their email ids in order to start collaborating. That's all there is in the name of setup.
Pro Free if you don't need the most advanced features
Most of its features are free, even video conferences. But also they have a Pro version with unlimited chat history, Active Directory integration among other things.
Pro Unlimited groups and teams
There is no limit on the number of groups or of group members. Similarly, within a team you can have unlimited members. There is no limit of number of teams too.
Pro Faster than Slack
Flock is offering an app that is faster than Slack.
Pro Highly configurable permissions
For every team, the permissions and restrictions can easily be set over the participating members and the conversations they are having.
Pro Better than slack
Pro Stickers
Posting messages is more fun with them in addition to emojis.
Pro Customisable UI, integrations surface just like native features
There are multiple options like slash commands, message buttons, chat buttons, attachment picker etc., where the integrations can surface inside the native app. This greatly eases the discoverability of a integration, making it really easy for the team members to find and use the integrations.
Pro Helps keep track of different conversations
Instead of rooms or channels Zulip is built around topics. This allows you to have multiple conversations at the same time without conversations interfering with each another. It also allows you to reference conversations without clutter.
Pro Free and open source software
Zulip is free and open source under the Apache 2.0 license.
Pro Easy asynchronous conversations
Its threaded model helps people working in different timezone's communicate effectively.
Pro Apps for every platform
Pro Hosted or on-premise
With data export tools so you can migrate.
Pro Intuitive interface
I struggled with Slack, never finding the settings I like to adjust. With Zulip never had such issues.
Cons
Con No thread feature
Reply command only quotes snippets. There's no implementation to show thread(s) of an initial message.
Con No End-to-End Encryption
Not even for private one-to-one messages, let along group chats.
Con Takes some getting used to
As most chat software uses the concept of channels or rooms, getting in the habit of splitting each topic off in a separate category can require some getting used to and discipline.