If you have a distributed team, and are using kanban as the project management methodology this tool, Trello, could be an interesting tool for the work. Trello allow you
set the definition of the various board for example, Backlog, WIP, Work pending test, released or some other flow as you deem the work to be. The tool allows embedding of documents at other locations, and fits with google docs quite nicely. It is possible to comment the work all along.

https://trello.com/


For some projects, I use trello. I own not stock, and get no remuneration from the company for my words. I write this in the hopes it is helpful.

Jon