New or changed features   

• Address Book now uses an iPad-like user interface
• AirDrop – Mac-to-Mac file sharing.
• Address space layout randomization – Address space layout randomization (ASLR), a security technique that puts important data in unpredictable locations, making it harder to target known weaknesses, is available for 32-bit applications, and "has been improved for all applications", in Lion.
• Auto-correction now behaves much like on iOS devices, displaying an iOS-like popup box.
• Auto Save – As in iOS, documents in applications written to use Auto Save will be saved automatically so users don't have to worry about manually managing their documents.
• Emoji support – Apple has added a new Emoji font commonly used in chat to express ideograms.
• FaceTime comes bundled with Lion.
• FileVault now offers full disk encryption added security with XTS-AES 128 data encryption. Support for FileVault on external hard drives has also been added.
• Finder improvements – Finder search offers suggestions, files can be grouped by various attributes, and one can now merge files under two folders with the same name – a prompt will appear asking whether one wants to replace or keep both files.
• Font Book 3—Font Book 3 now provides more flexible displays of character glyphs supplied by a particular font face. Duplicate font files are now flagged with a warning icon, and can be fixed automatically or resolved manually.
• Full-screen apps – Native, system-wide support for full-screen applications. Supporting applications display a new button at the top right of application window, this button opens applications in full-screen mode.
• High-quality multilingual speech voices – Apple allows you to download new high-quality voices in more than forty languages and dialects.
• iCal has an updated user interface, an annual view, and support for a full-screen view.
• iChat now has support for logging into Yahoo! Messenger. Users can audio- and video-chat with other iChat users using their Yahoo! accounts.
• Languages - Arabic, Czech, Turkish and Hungarian are added as full system languages, to make the total number of twenty-two languages available in Mac OS X.
• Launchpad – An application launcher that displays an iOS-like icon grid of installed applications. It features the ability to make multiple pages and group apps into folders that function the same as folders in iOS.
• Mac App Store – An application store built in the image of the iOS App Store. Like in iOS, it will provide ways for shoppers to discover apps, one-click installation of apps, and one-click updates of all or selected installed applications. Despite being announced as a future feature of Lion, the Mac App Store was released for Mac OS X Snow Leopard on January 6, 2011 as it was bundled with the Mac OS X 10.6.6 update.
• Mail 5 – Uses an iPad-like user interface, has a fullscreen-optimized view, uses chronological "Conversations" to organize messages, and supports Exchange 2010.
• Mission Control replaces the "All windows" Exposé feature. It gives an overview of all running applications just like "All windows" but groups windows from the same application. At the top of the screen it gives quick access to the Dashboard, Spaces, and running full screen applications.
• Multi-touch gestures – Similar to iOS, additional gestures performed using a multi-touch input device (e.g. Magic Mouse, Magic Trackpad) will allow the user to scroll, swipe to different pages, and enter Mission Control. While this is not the first official multi-touch support for Mac OS X, it has been expanded; other frameworks, such as Lux, have already created multi-touch support.
• Multi-User Screen Sharing—The built-in Screen Sharing feature now allows remote users to log into a separate user account from the one that is currently logged in. That means that while one user is logged into a machine, a second user can login to the same machine remotely, seeing their own desktop and user environment.
• Preview gains several features, including full-screen support and the ability to sign a document just by holding a signed piece of paper up to the camera.
• QuickTime re-incorporates some features from QuickTime Pro. New features cited include Copy/Paste, Insert Clip, Crop Video, Rotate Video, Resize, Trim, and more Export options.
• Recovery Partition – Apple has introduced a recovery partition that includes utilities generally found on the OS X discs. This partition will allow the user to restore their computer to its original factory state.
• Resume – Applications resume in the same state when re-opened as already seen in iOS. Because of this, the Dock no longer visually indicates whether an app is currently running or not by default – the original behavior can be restored in the Dock section of System Preferences.
• Safari – With full-screen mode and the new WebKit2 layout engine.
• System Information – This feature is a re-design of "About This Mac" and has been completely altered with new views which display graphical information on displays, storage devices, memory usage along with other hardware information.
• TextEdit gains a new graphical menu bar with font selection and text highlighting. The new TextEdit also supports Apple's new automatic file saving and versions technologies.
• Versions – Time Machine-like saving and browsing of past versions of documents for applications written to use Versions.
• Vertical text – Lion supports vertical layouts for East Asian languages.

Server features

• Wiki Server 3 – Making it easier to collaborate, share, and exchange information. Users can quickly switch between a server’s home page, My Page, Updates, Wikis, People, and Podcasts. File sharing is simpler, and a new Page Editor is added for easy customization.
• File Sharing for iPad – Lion Server delivers wireless file sharing for iPad. Enabling WebDAV in Lion Server gives iPad users the ability to access, copy, and share documents on the server from applications such as Keynote, Numbers, and Pages.
• Profile Manager – Profile Manager delivers simple, profile-based setup and management for Mac OS X Lion, iPhone, iPad, and iPod touch devices. It also integrates with existing directory services and delivers automatic over-the-air profile updates using the Apple Push Notification service.

Refinements to the user interface

• Redesigned Aqua user interface elements, button, tabs are now "sliding switches", progress bar. The red, yellow, and green close, minimize, and maximize buttons in the window decorations have been made smaller.
• Flexible window resizing from any corner or edge of the window.
• The metal finish has also been slightly altered. It is now a lighter shade of grey than before and features a speckled texture.
• By default, the dock no longer displays active application indicators.
• Autohiding scroll bars now disappear similar to iOS when they are not being used by default.
• Scrolling is reversed by default, to act more like a touch screen computer. (Content moves in the direction of finger movement on touch-pad or mouse)
• When resizing a window by clicking on the green button (left-top), a transform-effect animates the enlargement.
• New windows fly to the front (like opening a program in iOS).

Dropped features

• Front Row
• A Java Runtime Environment (JRE) is no longer installed by default, but can be installed on demand.
• Adobe Flash Player is no longer installed by default and must be installed manually.^{[citation needed]}
• Rosetta, software which makes possible the execution of PowerPC software on x86 hardware, is no longer available.