interactive "Documentation"

Well, these are not strictly sources of documentation, but rather sources of information.
But I think it fits in quite nice into this category.

You can talk/write to other zsh users on IRC:

• #zsh on freenode
• #zsh.de for our german audience… on freenode, as well.
• #zsh-fr for our french audience… you guessed it, on freenode.

…and via Email:

• zsh-users

If you need to reach the developers of the shell (eg. if you've found a bug):

• zsh-workers

The above links to the mailinglists are links to their respective web-archives.
Instructions on how you can subscribe, can be found here.

• For French speaking people, a list is available here