If you want to include DragThing, it's still probably a good idea to get in touch to check that you have the latest version.
If you want to distribute DragThing with a commercial product, let me know and we'll come to some arrangement. Individuals are encouraged to freely distribute DragThing and upload it to online services but commercial distribution is not permitted. For-profit shareware/PD software libraries are specifically prohibited from including DragThing on their disks, but genuine user groups are allowed.
The complete DragThing folder including this documentation and the unmodified application must be included with any distribution.
While DragThing may be distributed in the above cases, it is copyright and not in the public domain.