Good question. A submission can only be submitted to one of the categories. When submitting, you will be required to select the category that best fits.
However, you can submit multiple applications as long as they are unique. The rules state, "Multiple Submissions: A Maker may submit more than one Submission, however, each Submission must be unique and substantially different from each of the Maker’s other Submissions, as determined by the Poster and/or the Administrator."
Sure! Your category choices are: Office Add-in, SharePoint Framework web part, Office 365 App, or Mobile Office App. You can see more details on each under the How to Enter section on the rules tab: https://hackproductivity.devpost.com/rules
You can submit anytime until January 31, 2017 (5:00pm Eastern Time). Please try to submit at least a few days early if possible. If there is enough time, we will review submissions for eligibility and let you know if you are missing any items that would prevent you from being eligible. You can continue updating the submission form up until the final deadline.