I have seen many people trying to find a checkbox field for dynamics CRM forms and have seen lot of unsupported ways of people
trying to achieve one.
Dynamics CRM comes with this feature anyways.
What you need to use are two option fields with some formatting magic:
I am taking the example of a custom form and have put a custom field of type two options called Two options test:
1. Default format of the field:
2. Applying the checkbox look and feel:
Go to Form Editor->double click the field or choose Change properties -> Choose Formatting Tab-> See the section titled Control formatting-> Change it to Checkbox:
Save and publish the form.
The effect is below:
Hope it helps and Happy CRMing!