Some people still use Outlook. And whenever they send you something like an attachment or appointment, it shows up in your Mail with a winmail.dat file attached. (Ugh.)

But Letter Opener seamlessly converts all types of Outlook’s irksome winmail.dat files. (Hooray!)

License: Letter Opener comes in three versions: Letter Opener Pro ($29.95), Letter Opener Lite ($9.95), and Letter Opener Mobile. (Free)

Requirements:
OS X 10.6+
Intel