From Mac Guides
Lion is the codename for Mac OS X 10.7. Released on July 20, 2011, it is the eigth major release of Apple's Mac OS X Operating system. It was the first iteration of Mac OS to be distributed primarily via the app store (Apple online software distribution channel). Apple later announced an alternative distribution model involving purchasing a USB flash drive containing the OS, priced at US$29.99.
Changes and New Features
iCloud (formerly iTools, .Mac and MobileMe) is a cloud computing service from Apple Inc. announced on June 6, 2011 at the Apple Worldwide Developers Conference (WWDC). The service allows users to store data such as music files for download to multiple devices such as iPhones, iPods, iPads, and personal computers running Mac OS X or Microsoft Windows on computer servers owned by Apple. It also replaces Apple's MobileMe program, acting as a data syncing center for email, contacts, calendars, bookmark, notes, to-do lists and other data. 
Applications resume in the same state when re-opened as already seen in iOS.
Replaces the "All windows" Exposé feature found within Snow Leopard. 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.
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.
Lion-to-Lion direct file sharing via Wi-Fi Direct. No wireless access point required.
Mac OS X 10.7 represents a major security overhaul according to researchers who spent many months analyzing the OS. In particular, features such as full support for address space layout randomization (ASLR), application sandboxing, and a revamped FileVault encryption system as being key to Lion's improved security.
- x86-64 CPU (Macs with an Intel Core 2 Duo, Intel Core i3, Intel Core i5, Intel Core i7, or Xeon processor.)
- At least 2GB of RAM
- Mac OS X 10.6.6 or later (Mac OS X 10.6.8 recommended)
- 7 GB of free hard drive space is recommended
- AirDrop is supported on the following Mac models: MacBook Pro (late 2008 or newer), MacBook Air (late 2010 or newer), MacBook (late 2008 or newer), iMac (early 2009 or newer), Mac mini (mid 2010 or newer), Mac Pro (early 2009 with AirPort Extreme card and mid 2010 or newer).
|Mac OS Versions|
Classic (prior to Mac OS X) | Mac OS X (Pre-release) | Mac OS X 10.0 (Cheetah) | Mac OS X 10.1 (Puma) | Mac OS X 10.2 (Jaguar) | Mac OS X 10.3 (Panther) | Mac OS X 10.4 (Tiger) | Mac OS X 10.5 (Leopard) | Mac OS X 10.6 (Snow Leopard) | OS X 10.7 (Lion)