Apple announced that Mountain Lion will be available in July for US$19.99. Upgrades to Macs purchased as of today will be free. Any system going back to Snow Leopard can update at this price.
Several of the new features for the upcoming release of Mountain Lion revolve around iCloud, including Reminders, Messages and Notes. There will be Document-based apps as well, with document libraries available and updated across all Apple devices. This includes Pages, Numbers, Keynote, Preview and TextEdit. The notification center also will be added with a number of changes from the version currently in iOS.
The Mac is gaining dictation in Mountain Lion, which can be used in third-party applications.
Safari will have Twitter and other sharing options built into it, along with a unified search tool and syncing of tabs among all Apple devices.
A new feature called Power Nap will update your Mac while it sleeps, but it's only available on certain models. Other features include AirPlay Mirroring, the GameCenter and several features were added specifically for Chinese markets including new input messages and support for Chinese social networks such as Baidu.
We will have a full look into these Mountain Lion features throughout the day.