Basic, basic scheduling app

For my website I need a BASIC scheduling/reservation app that will let the end user select two fields based on my availability: date and time. Much like a hotel reservation website, there would be a drop down calendar to choose date, and the time availability on that date would be set by me (based on when I am free that day). The key thing is that once a user selects a date, the next user should not have the option to select that same date.