https://support.google.com/webmasters/answer/183668?hl=en
Both dropbox paper and google docs provide good 'whiteboard' solutions for sharing team knowledge and collaboration. I tend to prefer dropbox paper because it allows you to export to markdown (although not without some limitations).
One key function to consider on any option is how well the search works. Also, keep in mind the more 'free form' the tool, the more the tool will quickly become difficult to manage unless you set some ground rules at the start.
RE: Dropbox
I know a lot of companies are no longer allowing dropbox into their networks due to security concerns (it makes it very easy for an employee to take lots of internal documentation outside the company), and I believe at least one person needs to have dropbox pro ($99/year). Be forewarned dropbox may require users to have a paid account to access it in the future, although because it's still in beta, anyone can use it as long as they are invited in (I believe).
Here are some other options to explore:
I continued to expand on this idea this morning. I guess it struck a chord because it is something I struggled with for a long time in my own business. Imagine trying to disseminate a mountain of dynamically changing data to clients. As publishing has been in a hyperstate of change for the last 10 years, as soon as something is written, it's often outdated. Our own collective doc management improved when we implemented a few key items: