There is a 3rd alternative...
Atolia, the one and only workspace your team needs
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Why choose ChatWork or Zulip?
On the other hand, Zulip is an open-source platform aimed at the tech industry. It offers a free version, but no free trial, and includes features such as 1-1 and group video calls, screen sharing, recording, participant permissions, and end-to-end encryption. It also has unique features such as whiteboarding, newsfeed, and branding removal, but lacks certain features like contact management, task management, and a dedicated CSM. Additionally, Zulip has the ability to import data from other platforms such as Slack, Gitter, Mattermost, and Rocket.Chat.