Open Source Software Engineering Tools

I began working on my masters in computer and information sciences this year, hopeing that one day I can get my doctorate. I have been attending college or university for the past 6 years and it has not been an easy task. This semester is no different. I am working on a presentation about computer aided software engineering tools, specifically those that are for requirements gathering. I am looking for the best Open-Source Tool for this front end software development task that has a web based component or is fully web based. I would prefer suggestions on those that are fully web based and are free.

If anyone has any suggestion, please post them here. I want one I can install and actually use as my primary requirements gathering tool. Thanks in advance.