Digitally Sign Documents with Preview
Invoke Dictionary with a Keystroke
Find Menu Bar Options Quickly with Help
Add Handwriting Recognition with Ink
Optimize Your Wi-Fi Network with the Diagnostics Tool
Unless you've had problems with your Wi-Fi network, you've probably never seen OS X's Wi-Fi Diagnostics tool. That's because it's hidden away. To get it, Option-Click the Wi-Fi signal in your menu bar and select "Open Wi-Fi Diagnostics." This brings up a help wizard that you can ignore. On Mavericks, hit Cmd+2 to open up the diagnostics tool. On older versions of OS X, hit Command+N. You'll see a report with a ton of information about your networks, including all the other networks in your area. From there, you can follow these instructions to optimize your network for better performance.
Record Screencasts with QuickTime
The bulk of us don't need to record screencasts often. So, it's handy that the version of QuickTime included with OS X 10.6 and above does basic screencasting. With it, you can record your screen, voiceover audio, and do minor edits. Open up QuickTime and click on File > New Screen Recording to get started. QuickTime isn't our favorite screencasting by any means, but it does the job for free and works pretty well.
Speak to Your Mac with Dictation
For years, dictation software was always pricey and didn't provide the type of system-wide support that most people needed. With the release of OS X Mountain Lion, Apple included dictation right in the operating system and it works well. Everyone talked about the new dictation feature when it was first announced, but over time it has disappeared into OS X a bit. If you haven't messed around with it in a while, head into System Preferences > Dictation & Speech to get started.