With the change of name to Presence, the application has also moved from version 1 to version 2, introducing major new features like file sharing. You can read about these new features in the News section of Presence's main window on your Mac.
It's common to charge for major upgrades — if you use a few applications you'll probably have come across this before. If you don't, you might not know about upgrades and the fee might come as a bit of a surprise.
As with most applications, upgrading is much cheaper than the original purchase — for Presence, it's $15 to upgrade, while the full price is $40. (Upgrading is $25 if you have a family licence.)
To make sure recent purchasers aren't caught out, upgrading is free for people who purchased FarFinder after July 2010.
Finally, if you don't want to pay the upgrade fee and don't want the new features, you can download version 1 in the downloads section.