rmtoo - rmtoo is a free and open source requirements management tool.
ReqView - Simple and powerful requirements management tool enabling easy requirements gathering, traceability tracking and offline collaboration.
Doorstop - Requirements management using version control.
Jama Connect - The Leader in Requirements Management Solutions
Requirements Quality Suite - The Systems Engineering Suite offers you the tools, processes and skills to Verification, Traceability, Reusability and Quality.
Modern Requirements Suite4TFS - Modern Requirements Suite4TFS is an innovative, efficient and collaborative requirements management tool.