That is a new call-transfer feature. Select More > Call Transfer to transfer an ongoing call to another Skype user on their contact list, which could be useful in an office if you use Skype to save on the phone bills.
Beyond that, Skype for Mac 2.6 includes a number of other feature previously available elsewhere, but not on the Mac. These include joining public chats, chat typing indicator, Skype Prime (paying for a premium-rate line with Skype credit), automated updates and DTMF tones for automatic answering services.
Skype for Mac 2.6 is available for download now.