Initially, we used BitBucket, where we host our code, as both an issue tracker and also a Wiki. We would just put all the technical information within the repo's README files. If there is too much of text to be written in there, we would create a Google doc, copy the text in there and leave a link to the doc in the README.
But as we grew, our information sharing needs grew as well. The BitBucket repo README files weren't sufficient anymore. We needed a better tool to create, manage and share the info.
As a long time user of Atlassian products, it was a no-brainer for us to migrate to Confluence as our internal wiki and collaboration tool. Jira + Confluence + Hipchat together has improved our team productivity a lot.
Good luck! :)
After reading what I had posted, I feel that I sound more like a salesperson for Atlassian. Just wanted to leave a disclaimer that I am just a happy customer.