"Zulip Cloud Standard is free for open source projects and affiliated institutions."

which I thought was unambiguous that our paid plan is free for open source projects.

The intent of our pricing model is to charge businesses $80/employee/year for use by full-time staff. If you're a business that can afford to hire people, you can definitely afford $80/employee/year (under <0.1% of that employee's all-in cost to the company) for a productivity tool. Our pricing is free for open source projects and highly discounted or free for situations where the users aren't full-time staff (e.g. education).

If there's something we could do to be more clear in our pricing page, I'd love to hear it.