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Apple - OS X Lion - Learn about the top new features.
The Wayback Machine - https://web.archive.org/web/20110726192038/http://www.apple.com:80/macosx/whats-new/

Full-Screen Apps

OS X Lion offers systemwide support for gorgeous, full-screen apps that use every inch of your Mac display. You can have multiple full-screen apps open at once — along with multiple standard-size apps. And it’s easy to switch between full-screen and desktop views. Learn more about full-screen apps

Mission Control

Mission Control brings together full-screen apps, Dashboard, Exposé, and Spaces in one new feature that gives you a bird’s-eye view of everything on your system. With a single swipe on the trackpad, your desktop zooms out to Mission Control. Think of it as the hub of your system: View everything and go anywhere with just a click. Learn more about Mission Control

Mac App Store

The best way to discover apps for your Mac is now on your Mac. Just like the App Store on iPad, the Mac App Store lets you browse and download thousands of free and paid apps that you can start using right away on all your Mac computers authorized for personal use. New apps install in one step right to Launchpad, and the Mac App Store keeps track of your apps and tells you when updates are available. Learn more about the Mac App Store

Launchpad

Launchpad gives you instant access to all the apps on your Mac. Just click the Launchpad icon in your Dock. Your open windows fade away, replaced by a display of all your apps. Arrange your apps any way you want, group them together in folders, or delete them from your Mac with ease. And when you download an app from the Mac App Store, it automatically appears in Launchpad, ready to blast off. Learn more about Launchpad

Resume

Now apps you close will reopen right where you left off, so you never have to start from scratch again. And when you install software updates, you no longer need to save your work, close your apps, and spend valuable time setting everything up again. With Resume, you can restart your Mac and return to what you were doing — with all your apps in the places where you left them.

Auto Save

It’s time to stop worrying about saving your work. Because now your Mac automatically saves what you’re working on so you don’t have to. It’s not just an improvement for OS X, it’s an improvement for anyone who’s ever lost hours of hard work after forgetting to press Command-S. Learn more about Auto Save and Versions

Versions

Versions is a new feature that charts the history of your documents, taking snapshots in time, and displaying them side by side with the latest versions in an easily browsable timeline. You can review the past iterations of your compositions, restore a previous version, or copy and paste from old versions to new ones. Learn more about Auto Save and Versions

AirDrop

Looking for a fast way to share files with people nearby? With AirDrop, you can send files to anyone around you wirelessly — no Wi-Fi network required. And no complicated setup or special settings. Just click the AirDrop icon in the Finder sidebar, and your Mac automatically discovers other AirDrop users within about 30 feet of you. To share a file, simply drag it to someone’s name. Once accepted, the fully encrypted file transfers directly to that person’s Downloads folder.

Mail

OS X Lion introduces a whole new take on email. Mail puts your entire display to work with a gorgeous widescreen view featuring a full-height message and a message list that includes snippets. Conversations presents messages from the same thread in an elegant timeline showing each communication as it was sent while hiding redundant text. Mail also features search suggestions and search tokens, which help you find the messages you’re looking for fast. And a new favorites bar gives you easy access to the folders you use most often. Learn more about Mail

Lion Server

OS X Lion Server includes a host of enhancements that give you more control of your Mac server and the users who access it. The Server app — new in Lion Server — features a setup assistant that walks you through the server configuration process step by step. So now anyone can turn just about any Mac into a server. Profile Manager lets you remotely manage computers running Lion and iOS devices such as iPad and iPhone. You can even send updates to your users wirelessly via push notifications. Lion Server also adds file-sharing capabilities for iPad; includes improvements to Wiki Server, iCal Server, and Mail Server; and comes with Xsan built in. Learn more about Lion Server