Atlassian have a special at the moment where you can get 5 user licences of Jira and/or Confluence for $5 US (+GST) each
We've been using Jira
, their bug and issue tracking software, for a while now and it's been amazing. It's made things so much easier around here keeping track of everything. Definitely worth the investment for us.
We've only recently bought Confluence
which is their enterprise wiki solution, so we haven't had much experience with it yet, but it looks very promising. The fact that it can import Word documents and turn them into Confluence pages, and vice-versa, is going to make dealing with a lot of our customers much simpler.
I recommend them both.