Unknown to many people, Apple handed out devices running its latest OS X Mavericks operating system to select members of the press and media after announcing it back at WWDC, and early reviews and previews are starting to flow in.

As soon as the developer preview hit the web, we dove in and looked for subtle changes from Mountain Lion and found things such as LinkedIn integration, a Messages tab in Notification Center, an option in the menu bar to see what apps were draining your battery power, and much more. We also covered new dictation features in Mavericks. Via an option in System Preferences, there is now the ability to download a file and have offline dictation capabilities. One of the biggest selling points about Mavericks are the new multi-display capabilities, such as the ability to access the dock and menu bar across all of your monitors.

David Pierce of The Verge says that in Mavericks, multiple display support works like it always should have:

While most under-the-hood features of Mavericks will go unnoticed to the vast majority of users, these are actually some of the biggest changes. Between the supposed improved power management and new features for monitoring which app uses the most power, Safari also received a handful of performance improvements, as noted by Brian Heater of Engadget.

It’s all pretty seamless, and the setup feels like it should have been all along. If you use multiple monitors, you previously had to choose between using Apple’s cool features and actually taking advantage of your two monitors. Now it just works.

While the overall design of Mavericks is largely the same as its predecessor, many of the standalone apps have been redesigned to reflect the new “flat” design Apple is going for with both OS X and iOS 7. For example, all the linen backgrounds are gone, the Calendar app has a cleaner design, there are several UI tweaks in Safari, the Notes app is simpler, and much more. You can look through our full image tour here.

Jim Dalrymple of The Loop wrote that while he doesn’t care for some the chaged UI elements in Mavericks, they make sense in Apple’s plan to get rid of skeumorphic design.

Our own Michael Steeber also went hands on with the totally new Maps app for Mavericks. The Maps app provides the same 3D flyover capabilities that we all know and love from iOS as well as detailed directions to a location. One of the coolest features is the ability to send directions directly from your Mac to an iOS Device.

I find Calendar and Address Book a bit too stark for my tastes. It’s like loading a Web site without the CSS—it seems like there was too much taken away. However, I don’t mind Notes. Maybe it’s just the fact that they left some color in there that makes it work for me.

Vincent Nguyen of SlashGear praised Apple’s efforts of continuing to integrate OS X and iOS, notably in the new Maps app.

The second developer preview of Mavericks went live late Monday night, though not much has changed from preview one. We noted things such as improved performance, minor UI tweaks in Safari, an iCloud Keychain setup prompt, and more.

Apple says OS X Mavericks will go live in the Mac App Store sometime this fall and the company is already testing it throughout Cupertino and Apple retail stores.