docTrackr encrypts your documents before you share them with others, and lets you set privileges so only your intended recipient can open and read them. You'll also receive notifications when someone has opened the document you shared, so they can't play the old "I never got it!" game with you.
If you've ever wanted to send something confidentially to a friend, family member or coworker, but you also didn't want to jump through hoops to make sure they could decrypt it, docTrackr makes it easy. You can also set privileges and permissions for the recipient, so they can read it but they can't just forward it to someone else, for example. Just upload the document you want to secure, add your recipients, and select whether you want those people to be able to view the document, view and print it, or edit and print it. (You can see all of docTrackr's supported file types here.)
When your recipient opens the document, you'll be notified, and you can visit the document's page in docTrackr to see how many times they've viewed it, if they've made changes, if they've tried to forward it, and even where they've viewed the document from. If you're sharing a sensitive document with multiple people, you can even see all activity on the file. We tried the service out, and it works as promised -- sharing documents is easy, the security controls worked as promised, and it was fun watching exactly when someone opened the file you sent to them.
docTrackr definitely has a business edge to it, but it's useful for individuals too. Even if you just work with someone who's notorious for pretending they "never got your email" with the files you need them to work on, it can be a lifesaver.