The newest Apple operating system, Mountain Lion, won't make its way to the masses until this summer, but developer nerds have gotten their hands on it, letting us in on the best (and worst) parts of our computer's future brains. If last July's Lion release made Macs look more like iPads, this year's upgrade will make them look more like iPhones. The new OS borrows lots of tricks from the newest iOS. And, considering the popularity of those little pocket computers, it's no surprise that the developers are loving it. 

General Impression

This is more than just a spruce up, writes The Verge's Nilay Patel. "It's a ton of stuff; Mountain Lion is very much a major new version of OS X, not just a polish-and-stabilize job like Snow Leopard."

Apple's making a move to integrate all iGadgets, adds TechCrunch's MG Siegler. "They view it as the next step towards a more unified Apple ecosystem." 

Making it similar to iOS adds a nice familiarity continues The Loop's Jim Dalrymple. "If there was a theme in Mountain Lion, I’d have to say it’s familiarity," he writes. "Apple brought many new features into the new operating system from iOS, so millions of users will recognize the names of the apps and features. "

The update cleans up inconsistencies over platforms, says Daring Fireball's John Gruber:

The recurring theme: Apple is fighting against cruft — inconsistencies and oddities that have accumulated over the years, which made sense at one point but no longer — like managing to-dos in iCal (because CalDAV was being used to sync them to a server) or notes in Mail (because IMAP was the syncing back-end). The changes and additions in Mountain Lion are in a consistent vein: making things simpler and more obvious, closer to how things should be rather than simply how they always have been.

Messages

Apple has updated iChat to appease iMessage users, according to Siegler. "It technically replaces iChat, but with some tweaks, you can find that old interface as well. But the focus now is on a unified dashboard of all your messages, meaning yes, iMessages as well as IM messages. Heavy iMessage users are going to love this."

That means integration, continues Dalrymple. "Here’s the great thing about Messages. It keeps the conversations synced between devices."

But that also can lead to problems, adds Patel:

The first problem is simply structural: not everyone uses iMessage for everything, and it’s easy to find yourself looking at an unwieldy mix of iMessage, Google Talk, and AIM messages all from the same person at the same time. People use different message services for different things, but Messages wants to mix everything together in a way that doesn’t always make sense — and only iMessages will sync across devices, so you might find yourself missing pieces on iOS devices. iMessages sent from iPhones that fall back to SMS also won’t show up, which can be confusing. 

Notifications

A new take on Mac notifications, writes Patel. "Mac users have relied on the excellent open-source Growl notification system for years now, so the addition of Notifications Center to Mountain Lion seems a bit anticlimactic at first glance. But look a little deeper and it's clear that Apple has a very different idea about how notifications should work — an idea that's unsurprisingly almost exactly how they work in iOS 5."

Slicker than Growl, adds MacWorld's Jason Snell. "Apple’s take on the concept is slicker than Growl, though, and if it ends up being supported by more programs, it’ll be an even bigger boon."

iCloud

Even better than Lion, says Siegler. "With Lion, iCloud had a number of points of integration. But they were tacked on after the initial release. With Mountain Lion, the connection is much deeper. Actually, from the first screen in the setup assistant, you’ll now be asked to set up iCloud."

The whole connection process is seamless, from Dalrymple "The iCloud integration is superb. It’s not just registering your computer, Apple made it so iCloud sets up many of the applications and services on your system for you ... For example, iCloud in Mountain Lion works with Mail, Contacts, Calendars, Messages, FaceTime, Notes, Reminders, Game Center, Mac App Store, Documents and Data, and Bookmarks."

It just makes sense, says Gruber.  

I remain convinced that iCloud is exactly what Steve Jobs said it was: the cornerstone of everything Apple does for the next decade. So of course it makes sense to bring iCloud to the Mac in a big way. Simplified document storage, iMessage, Notification Center2, synced Notes and Reminders — all of these things are part of iCloud. It’s all a step toward making your Mac just another device managed in your iCloud account. 

Airplay Mirroring 

The best totally new feature, in Dalrymple's opinion. 

Perhaps one of the coolest features of all in Mountain Lion is AirPlay Mirroring. This feature wirelessly sends what’s on your Mac to an HDTV using the company’s Apple TV device. Mirroring sends a 720p video stream with audio ... Typical of the way Apple does things, they took all of the technical mumbo jumbo out of the picture, so it just works.

A step in the right direction for the streaming TV gadget phenomenon we're all waiting for believe Gizmodo's Sam Biddle and Adrian Covert

Finally, we now have the ability to push our computer screens to our televisions (provided you have an Apple TV). Mirroring is limited to 720p resolution and stereo audio, but that should be fine for most. Sadly the feature seems limited to mirroring, and not pushing system (or app-specific) audio to AirPlay speakers or Airport Express, but it's at least a step in the right direction.

Gatekeeper

More security for app downloads, explains Patel. "Apple's introducing Gatekeeper, which can only be described as a bold new middle ground for app distribution: an optional setting in OS X 10.8 allows users to restrict their systems to run only apps that have been signed by trusted developers using a free certificate provided by Apple. "

And not everyone's going to like it explains AllThingsD's Arik Hasseldahl.

Expect this feature to be controversial among Mac software developers. Basically, it’s an attempt by Apple to deal with the fact that the one serious security threat it faces is software that looks good at first but turns out to behave badly only after you’ve downloaded and installed it. The new scheme basically sets up a three-tier system, where the user can decide from where they will be allowed to download and install new software. In the most restrictive -- or some will argue safest — case, you can set your Mac to allow only software from the Mac App store.

Other Fun Stuff  

The new OS will also have Twitter integration, the iOS inspired share sheets(arrow function picture below), the iOS Reminders app, and a games center.