I am currently using an open source tool for requirment analysis , which is termed as Arbiter.
It is basically, a requirements gathering and verification tool for web projects. It's aim is to sharpen the communication between stakeholders and developers.
Arbiter itself runs as a simple document repository on a web server. When requirements documents are added or updated, they are scraped of test cases and these tests are run. Tests are just examples of how someone would use a web browser to get information from the site.
Please update me about any other features of this tool.I also mention this founding in my blog also.