Checkboxes that allow user input

You can do something very similar by using the multiple choice fields, a single input field and the conditional logic.

I did a quick demo a couple of days ago, you can check out this thread and the screencast link on my last post.

http://forum.gravityhelp.com/topic/add-other-text-input-field-to-multiple-choice-selection

@beyoyo2 Send us a WordPress admin login for the site having the issue and let us know which form and field so we can take a look at your configuration and see what you are doing.

I did not see anything come through at the info@ email address. Please send the information to use via our Contact Us form here: http://www.gravityhelp.com/contact-us/

The problem with your form is that field isn't appearing because you have applied conditional logic to it that is conditional based on it's own value. That isn't going to work, the condition can't be met because the user can't select the condition because it can't be met. You've configured it in such a way that it will never work. See this screenshot: http://grab.by/9ZKu

Your form is configured to show Field A if Field A's value = Other. Well that can never occur because Field A is hidden unless it's value is Other and since the user can't select Other it's value never is Other...

Conditional logic is applied to the field you want to show or hide. NOT to the field that triggers the show/hide.

So you'd add Field A and Field B and then you'd configure conditional logic on Field B to show the field if Field A's value = Other.