Free often comes at a cost. In terms of open-source test management tools, that cost is the quality limitation placed on your QA. Even the savings you seek by choosing a free test management source disappear if a critical bug is missed, your launch date is delayed or you are forced to make expensive fixes later in production.
While the well-established open-source test management tools have survived a decade or more in the software testing industry, their role has been greatly reduced. The simple irony is, it is hard to achieve maximum QA value with a free product.