Sign up genius ability in a form?

I use another site called sign-up genius for enlisting volunteers and other applications where there are dates, times and a specific number of people I'm trying to recruit. So the webpage looks something like this the attached screenshot.

So there can be multiple dates, multiple times and multiple opportunities for people to sign up. But since we have many people signing up the form needs to somehow track what times are reserved already and only allow people to select open date/time/slots. I don't care if the previously reserved times are shown or hidden but a) I need the form to know what previous session/users have reserved b) allow people to only input to 'open' date/time/slots. I don't really care if the 'reserved' slots are hidden or shown but the form needs to track previous inputs.

If I understand you correctly, you want to have some kind of a reservation feature that let's you monitor the number of people signing up on a specific date or item, is that correct?

You could try the following widgets to do that.

For items, you can try using these ones:

http://widgets.jotform.com/widget/inventory 

http://widgets.jotform.com/widget/quantity_gift_registry 

http://widgets.jotform.com/widget/gift_registry 

http://widgets.jotform.com/widget/ticket_purchases 

If you want something like a calendar, you can try this:

http://widgets.jotform.com/widget/date_reservation 

Do let us know if this is what you are looking for.

Thanks.