What project/process management systems exist where participants cannot see each other?

Question

Startups

Something like Trello or Zenkit, but not to see each other, could not know about each other, contact each other.
You need features like Trello and Zenkit. It is important that you can assign tasks to participants and control the progress of the implementation (any of the options, for example, in the dialogue mode about the difficulties in completing it as comments)
Perhaps something like Redmine

Answer 1

could not know about each other, contact each other.

What will prevent them from writing their e-mail right in the comments to the task?

Answer 2

Closest analogues: Jira, YouTrack.

Answer 3

With the right settings, I think Meistertask is the best. There are no personal messages, but only the owner of the project can write to another person after looking at the information in the access details. See screenshot: jmp.sh/OPwSxJe

Answer 4

In jira, setting the appropriate view rights can be done.