I’ve used forms to conduct experiments in class, to collect information about my students, and to create surveys for campus committees, but it just dawned on me yesterday that I could use forms to help track recommendation letters for students. I set up a Google Form (Sean has a nice video tutorial if you have never done it before) that collects the information I usually like to know. When a student asks me to write letter for them, I can email them a link to this form.
As they decide to apply to a school, they can fill out and submit the form, and all the information will be added to one spreadsheet that I can sort by student name and due date. I also added a column to the end that I can fill in after I submit a recommendation letter. If you were comfortable with students seeing who else you are writing letters for, you could give your students viewing privileges for the spreadsheet, so that they could check and see if you had submitted their letter or not.