There are several changes from past versions of OS X. The most notable is that the entire OS is shifting to iOS. The Lion server is built into the base OS X 10.7 Lion distribution and is free.
“Lion Server guides you through configuring your Mac as a server,” Apple said.
“And it provides local and remote administration — for users and groups, push notifications, file sharing, calendaring, mail, contacts, chat, Time Machine, VPN, web, and wiki services — all in one place.”
Another useful feature on the firmware level is the inclusion of “Trim.” This feature only applies to users of solid-state drives. It revamps garbage collection to prevent write speed degradation on blocks users previously wrote to. The net result should be better SSD performance over time.
Another new feature is "Air Drop,” an app that allows you to transfer files over wireless networks by a simple drag and drop interface where users can auto-locate nearby users with Air Drop enabled.
Apple has also added the ability for multiple users to be remotely logged in to a machine at once. Previously if another account was logged into a user’s remote OS X machine the user could only enjoy a movie of what they were doing. Now they can do that or login in parallel via their account.
Another new app is Podcast Producer that was previously only available to "pro" paying server users. The app is similar in nature to Garage Band, allowing for users to more easily create podcasts.
A new feature called "Signature Capture" lets users write a signature (on paper) and then hold it up to the system's web cam. The shot is then captured and interpreted into a filtered image file. That image can be added to make official PDFs and other documents.