There were a lot of open source Scrum or agile project management tools development years ago. However, most of these projects have been abandoned for some years. Those remaining have switched to a dual open source/commercial model where the paying development supports the open source tools, even if this one has usually less features than its commercial “brother”.
For small teams or people that don’t necessarily need all the features of commercial Scrum tools, there are a lot of commercial vendors big (VersionOne, Rally, …) or small (TinyPM, ScrumDo….) that offers free version of their Scrum Tools.
You can find a list of commercial Scrum tools that you can use for free on http://www.scrumexpert.com/tools/using-commercial-scrum-tools-for-free/
