Doorstop - Requirements management using version control.
ReqView - Simple and powerful requirements management tool enabling easy requirements gathering, traceability tracking and offline collaboration.
rmtoo - rmtoo is a free and open source requirements management tool.
Jama - Jama combines requirement management software with enterprise collaboration capabilities to solve product delivery problems.
Reqflow - Reqflow is a free and open-source tool for traceability of requirements across documents, designed to analyse documents with speed and efficiency.
Jama Connect - The Leader in Requirements Management Solutions