Most of the time, I've seen release management handled as a defined process with the supporting tool as the version control system (usually via branching and tagging). However, are there any tools dedicated to release management? I'm looking for both open source and closed source tools, if any exist.
Release management transcends tools, but that doesn't mean you can't put together an environment to support your RM processes and strategy. We rely heavily on Visual Studio TFS for our RM approach, since it supports build automation, SCM, QA (testing), and integrates with SharePoint 2007 for documentation purposes.
Our RM workflow is hosted in SharePoint as well. This is all very dependent on the Microsoft stack, obviously, but there are equivalent OSS tools.
ETA: Our RM approach is based somewhat heavily on ITIL v2, so it might be more rigid than what you are asking for.