Raul,

It seems best requirments for you would be a web based tool that can help you with requirments management, definition and colloboration.

Recently I came across a new tool, Clariys, www.clariys.com that is web based. Unlike other tools that focus on organizing requirements, Clariys also helps you to define the complete requirements and in format you prefer,  Plus Collaboration is easy as it is web based. Following is high level product overview from the Clariys website:

With Clariys you can -

1. Capture high level- requirements  feature backlogs, ideas, customer requests
   a. With ability to modularize and logically group requirements in a hierarchy
   b. Plus ability to manage, plan and prioritize at individual requirement level 
2. Analyze and Elaborate-  your requirements, using
   a. Text, Bullet Lists with rich text editor
   b. Use Case Diagrams with diagramming tool
   c. Activity & Flow Diagrams with diagramming tool
   d. Sketch Wireframes  & Mockups
3. Validate and Collaborate-  review requirements and visual artifacts with the team and embed comments.
4. Issue Management- track and manage issues & bugs related to your requirements.
5. Reporting- generate and export custom reports in CSV/Excel format with user-specified report inputs and sorting.
6. Change Control-  generate requirements baselines and compare versions