Apple unveiled the successor of Lion, aka Mountain Lion, expected public launched late summer 2012.
In a dedicated webpage, Apple provides some additional details and the clear convergence between Mac OS and iOS, as several iOS functions, including the new application Message that will replace iChat in Mountain Lion. Some Mac users might think that the iOSification of Mac OS X is a dangerous trend where the end users will lose full control on the system. Nevertheless, Mountain Lion will also feature Gatekeeper, a security management application that will allow digital signature of software and drivers, to avoid undesired activation by malware codes.
A beta version of Mountain Lion is available, as well as a public beta version of Message: http://www.apple.com/macosx/mountain-lion/messages-beta/