TestLink is most widely used web based open source test management tool. It covers both requirements specification and test specification together.
It supports both automated and manual execution of Test cases.Automation execution of test cases can be achieved using XML-RPC technique.
It supports multiple user login and parallely multiple projects can run in TestLink.
Role can be created based on project and organisation requirement.Features/menu's of TestLink can be mapped to newly created role irrespective of the role.
It can be integrated with bug tracking tools like Bugzilla and Redmine.
It also supports SMTP integration.
TestLink have bunch of reports to serve project and organizational needs.
Any role of TestLink can generate report to evaluate their performance.