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