While Avid once offered a 30-day free trial of Pro Tools 10 and Pro Tool 10 HD, the offer has been updated to the more recent Pro Tools 11 and Pro Tools 11 HD, as of 2015. The free trial is available at connect.avid.com/pro-tools-trial.html.
An iLok account is required to access the free trial. An iLok is an electronic data storage device that allows access to all of the licenses a music professional requires. It plugs in to any device the same way a flash drive does, allowing the user to access all of his licenses through one system. While the iLok account is free, the physical device costs around $50 on iLok.com.
Pro Tools 11 also has system requirements that must be met in order for the program to run, even in the free trial version.