Helpsumo customer support software, while it isn't free is well worth it, and much better than the other options that you have listed.
I've been looking around for a good helpdesk, or more specifically, a customer service software that is cloud based and has a community with a knowledge base. Lastly it has to be ready to implement out of the box.
Here are my requirements
4. Knowledge base
6. A type of a feedback widget, like a support tab that's easy to find.
I know UserVoice, Zendesk and GetSatisfaction offer something like that - of course the latter lacking the help desk component.
So far in my search I've only ran across the Helprace help desk app - it seems solid and promising.
Are there any more examples out there, perhaps with social media integration?