Is there a way to run a report on any unfilled slots?

Under the Organization page click on the Reports Tab, select the Sign In Sheet Report, the Signup Sheet, or the One Slot Per Row Reports, and under the Options, click on the button next to “Include unfilled slots” as well as any other criteria you would like to have on the report.  Click on the events you would like to run the report on, and then click on the Run Report button at the top of the page.