Since you are looking mostly for the wiki part there is Dokuwiki which is magnitudes better at being a wiki. Remember, wiki is derived from the Hawaiian word for quick or something to that effect and whatever Confluence is it isn't quick.

Don't know how well it will hold up under scrutiny if black hats gets a reason to swarm over it, but unlike Confluence you can hire someone to patch the guts of it if necessary.

Edit: I have no reason to believe it is worse than anything else, I'm just pointing out it probably hasn't had so much exposure to help it harden.