I've used Google Calendar Appointments as a checkout system for our Building Tech Checkouts for the past several years. While overall this has worked well, there has been a few bugs and setting up multiple periods for checkout can be very time consuming.
I recently discovered two new resources that I am going to make a run at for the 2015 - 16 school year. Unless there is an update to Google Calendar I believe one or some combination of both might be a more efficient way to manage the checkout of devices.
CheckItOut is a Google Form Add-on that creates a question or multiple sets of questions for checking In and OUT of resources.
Lab Scheduler is a Google Sheet Add-on resource scheduler designed for schools, that uses periods or blocks to schedule rather than times.
What tools are you using to facilitate online checkout of resources?