Hightail

Hightail is a service that specializes in e-signatures and document delivery. It also bundles in a file-syncing service. With an account, you can use the Hightail Web app and mobile apps to digitally sign documents, as well as send documents to others to be signed.

Hightail has apps for Mac, Windows, Android, iOS, and the Web. Here you can see the Hightail syncing folder installed on a Mac. Right-clicking on any file brings up an option to send it via Hightail.

Similar to other syncing services, Hightail shows icons on all the files you sync to indicate whether syncing is still in progress (red) or complete (green; shown).

Hightail actually has two apps each for Windows and Mac, one that enables file syncing and another, shown here, called Express that gives you control over how you wish to share files. With a Hightail Professional account, you can password-protect files and set an expiration date for download links. For free users, download links expire in one week.

The Express app also lets you see and keep track of items you sent. This window also lets you see how many times the files you've shared have been downloaded.