Kerika gives you flexibility: For each board that you create, you can decide who gets to view it and who gets to make changes.
When a board is made Public, all the documents contained within it – on all the cards and canvases that make up that board – are also made viewable to the public.
Note: users of premium Google Apps, e.g. Google Apps for Business, cannot make their boards open to the public, because of limitations imposed by Google.
If you want all of your boards to always be accessible by the public, you can set that as a User Preference: