Not so long ago, Microsoft reported that older versions of Skype for Mac and Windows would soon stop working.
Now, in discussions (1, 2) on Skype Community (the company's discussion forum), users complained that they were no longer able to use the app on certain versions of Apple's desktop operating system, such as 10.5.8 and 10.7. 5.
In an official response, Microsoft made it clear that, from now on, Skype minimally requires OS X 10.6 to function and that users running OS X 10.6 (Snow Leopard), 10.7 (Lion) or 10.8 (Mountain Lion) must download version 6.15 of the application. To do this, simply visit this page using one of these versions of the system.
Anyone running OS X 10.9 (Mavericks) or the test version of OS X 10.10 (Yosemite) should use Skype 6.19 (the most current).
Update · 08/08/2014 s 13:52
A Skype representative told the 9to5Mac that the company will make available a version of the application compatible with OS X 10.5 (Leopard) even though it has not given a notion of the release date. OS X 10.4 (Tiger) users, however, will have to upgrade to newer versions of the system.