TestRail’s web-based test case management is used by thousands of great QA and Development teams to efficiently organize, track and manage software testing.
In my experience, this is the best, because it is very easy to organise your working process. I like the system of filters and boards it has. I have tried other stuff too, like Asana, Jira, even Monday. Those have their pros and cons too, but to me personally Youtrack is the preferred one, due to it's simplicity and inherent minimalism. I don't do rocket science, so maybe that's why I find it the most compelling.
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