It also allows you to specify whether your Mac will install apps only from the App Store, from the App Store and this list, or from anywhere you want. If you choose the Mac App Store only, you'll be able to make sure that everything you install has gone through Apple's approval process, which is about as protected from malware as you can get.
When you installed Mountain Lion, every app that was already on your Mac got a free pass as far as Gatekeeper is concerned. The apps were grandfathered in as already having been run and cleared; since Gatekeeper works by preventing the first launch of an app, those apps are OK. In fact, you can keep the "Mac App Store and identified developers" setting turned on for safety while still installing and running non-signed apps; just right-click (or control-click) the unsigned app and choose Open. Gatekeeper will prompt you for a single-app exemption and if you're OK with it, the app will launch from then on.
Now, not everybody appreciates Apple's "walled garden." Some developers take issue with the fact that they need to be "verified" by Apple before releasing and running software on the Mac. Gatekeeper is also responsible for "sandboxing" applications, which means keeping applications from changing files on parts of your computer that they don't usually interact with (though this does cause problems for apps that do want to dip into your personal system files, usually just to make things easier on you).
At any rate, sandboxing and Gatekeeper are a reality for now. If you want to tweak your Gatekeeper settings, you can find them in the System Preferences screen under Security and Privacy.
Mute Notification Center Alert Sounds in OS X Mountain Lion
Notification Center is a great addition to OS X Mountain Lion but the alert sounds can be pretty annoying if you have a lot going on. Rather than muting all system audio to hush the constant chiming, you can directly silence notifications on a per-app basis.
Open System Preferences from Apple menu and click the “Notifications” menu
Select apps from the left and uncheck the “Play sound when receiving notifications” box
Repeat for every app you want to silence
This better than disabling Notifications completely because you’ll still see them arrive, but you won’t bother your coworkers with beeps and boops anytime it’s your turn in Chess.
I don't know of a way to turn off alert audio for all notifications in OSX. At least not yet anyways.
Wi-Fi Scanner Tool is New in Mac OS X Mountain Lion, Here’s How to Use it.
The already powerful Wi-Fi Diagnostics Tool in Mac OS X got a redesign in Mountain Lion and with it came some new features that make it better than ever. One of the best new additions is the built-in Wi-Fi scanner tool, which is a full-featured wifi stumbler to find and discover nearby Wi-Fi networks – even those that don’t broadcast their network names.
This is really an advanced feature that has a wide variety of potential uses beyond just locating access points, most users would be best off just using the Wi-Fi menu to find available wireless networks to join. For those that want a wireless stumbler, here’s how to find and use it.
First you’ll want to make the Wi-Fi Diagnostics app readily available by bringing it to LaunchPad or the Dock, to do that:
From any Finder window, hit Command+Shift+G and enter the path: /System/Library/CoreServices/
Locate “Wi-Fi Diagnostics” and drag and drop it into Launchpad or the OS X Dock for easy access
Now that you have the Wifi app in an easy to find location:
Click the “Wi-Fi Scan” tab to get started with the wireless stumbler tool
Under the Wi-Fi Scan tool, you will see all available network names and their respective BSSID, channel, band, protocol (wireless n, g, b, etc), security type, their signal strength, and the noise level of the signal.
The tool defaults to scanning once and displaying the found information, but you can turn on Active Scan or Passive Scan mode to constantly search for new networks by clicking on the “Scan” pulldown menu in the lower right corner.
There are plenty of potential uses for this utility and the wireless stumbler, whether it’s optimizing networks, reducing interference and noise, or discovering those around you, but the wifi diagnostics app also includes many powerful features that allow you to capture network traffic, be it data that is sent from the computer in use or even all nearby wireless networks. Ultimately those later functions and their uses are far beyond the scope of this article, but previously Mac users had to use third party apps like Kismet or boot from a separate Linux installation to access advanced network capturing abilities.
Get Detailed WiFi Info From the Menu Bar M/ Lion as well
You can retrieve extended wireless connectivity data from anywhere within Mac OS X by holding down the Option key and then clicking on the WiFi menu icon.
Option-clicking will display a sub menu under your active wifi connection that shows what wireless band you are using (PHY Mode), the routers SSID (BSSID), what channel the wireless router is using, which encryption method (Security), signal strength (RSSI), the transmit rate, and MCS index (whatever that is).
You can also mouse-over other SSID’s to see a slightly more condensed version of this information. All of this can be helpful for avoiding potential channel conflicts, or when troubleshooting wireless problems.
Stop OS X Mountain Lion from Automatically Downloading App and OS X Updates
OS X Mountain Lion has a handful of features that are dependent on a constant internet connection, and one of those is the new automatic update feature. Undeniably convenient, OS X and all apps installed from the Mac App Store will automatically download and update themselves, but if you have metered internet or are using Personal Hotspot you’ll probably want to save the bandwidth and stop those updates from downloading themselves in the background.
Open System Preferences from the Apple menu
Choose “Software Update” and click the lock icon to unlock the preferences
Uncheck “Download newly available updates in the background”
Optional but not recommended: uncheck “Install system data files and security updates”
Leave “Automatically check for updates” enabled to behave like versions of OS X before 10.8, where the system would alert you to new updates available but would not download them without your permission.
You can also save bandwidth by disabling the automatic app downloads feature, which is borrowed from iTunes and previously only applied to iTunes media and iOS apps.
Manually Checking for Updates
With automatic downloads disabled you will have to manually install OS X updates and updates to apps from the Mac App Store, all of that is now done through the App Store itself, unless the app came from a third party.
Rename a File from an Applications Title Bar in OS X Mountain Lion
OS X Mountain Lion now lets you rename a file directly from the application it’s opened within. This feature is supported in most bundled Apple applications, including TextEdit, Pages, Preview, and others.
Hover over the files name in the title bar until the arrow appears
Click the arrow to pull down a menu, select “Rename”, enter the new name and hit the return key to save the files name change
The file extension remains consistent with the files format, and unlike renaming things in the Finder you can’t accidentally change the file extension too.
The quick video below demonstrates the process:
The usual methods of renaming files through Finder or the command line are still around, but if you’re saving files directly to iCloud this will likely be the preferential method from Mountain Lion onward.
Delete Mail in OS X Mountain Lion the Smart Way, Like Outlook
The Mac Mail app received a wonderfully understated change with how it handles deleting mail in OS X Mountain Lion. With the new version, deleting emails works more like Outlook; you delete an email and it then selects the next oldest email rather than jumping to the next most recent message. It’s a subtle change, but it makes a worlds difference when you are clearing out a cluttered inbox, letting you start at the top of a mail inbox and working your way down deleting as you go.
You can also delete mail like this in the Outbox and Sent folder too, though you’ll want to select “Sort by Date” > “Ascending” as the sort method.
With previous versions of Mail in OS X the behavior was exactly the opposite, deleting a message selected the next newest message, making you constantly have to use the arrow keys or select the oldest mail to delete things. Very frustrating for anyone accustomed to Outlook or for anyone wrangling a large inbox full of spam, making this a welcome change indeed.
If you need to use Java, installing the Java Runtime Environment (JRE) in OS X Mountain Lion is necessary even if you had Java previously installed in OS X Lion or Snow Leopard and just performed an upgrade to 10.8. That’s because Mountain Lion uninstalls Java during the upgrade process, this is to insure the newest version of the runtime is installed on the Mac for those who need it and leaving it out for those who don’t, theoretically preventing some potential security problems with Java like the old Flashback trojan.
Installing Java in OS X Mountain Lion is easy enough and can be done two ways:
When a Java app is opened in Safari or elsewhere you will be prompted to install Java for OS X (2012-004 currently)
Manual command line method to force the installation
The command line installation is fast and likely preferable for many advanced users since it can be initiated at any time, here’s what to do:
Launch Terminal from /Applications/Utilities/ and type the following command:
Hit return to see a message stating “No Java runtime present, requesting install” followed by a window prompting you to install Java SE in order to open “java”, click “Install” to get the latest version
Many Mac users won’t ever need to use Java and for the average person it may be best left uninstalled. Disabling java or leaving it uninstalled remains a decent security tip to protect a Mac against some of the rare trojans and viruses floating around out there.