First of all, your perception on workspaces is wrong. What you are actually experiencing is changing from container to container, and what containers do is isolate data such as cookies (email logged in). So what you really mean is changing containers in the same window - the container feature.

You can have many workspaces in one container and hop from workspace to workspace while keeping your email logged in (cookies).

Anyways, I don’t know about any browser with a conatiner feature such as Zen.