See https://github.com/cjbarber/hipchat-alternatives for more ideas.
Besides a gazillion open source wiki projects…
For a bigger far more all encompassing documentation toolchain:
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Jive Disclosure: former employer (but thoroughly recommend for the right culture/environment)
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Salesforce.com’s Chatter Disclosure: former employer (don’t recommend based on user experience 3+ years ago)
Another good chat alternative is [Discord](https://discordapp.com/. While it's not specialized for business it has many features that are very nice to have like voice channels and webhooks (with slack webhooks support)