4. Add clips from websites to Dashboard
Remember Dashboard? Introduced with 10.4, this overlay holds 'widgets' that can perform handy little tasks - Apple still hosts a catalogue of them at apple.com/downloads/dashboard. One oft-forgotten trick is that you can make your own widgets by clipping from web pages. The best bit is that the web page remains live. Here's how to do it (we're going to clip out some cricket scores, but it will pretty much work for any part of any site).
1. Navigate to the page you want to clip a section from in Safari. (It has to be Safari, not Chrome, Firefox or whatever.) You can clip out information that's essentially static - say, a list of keyboard shortcuts you want to refer to - or stuff that's changing all the time.
2. Go to the File menu and choose Open in Dashboard…; now you can mouse over sections of the web page, and it's usually smart about snapping to appropriate areas. If not, just click then drag the handles. Once you're done, click Add at the top right.
3. Once the clipping has been added to your Dashboard, you can click the i at the bottom right to flip it round. Here you'll see options for the frame; pick the one you like. The web clipping should update anyway, but if you need to force a manual refresh, click it, then tap Command+R.
5. Type exotic characters
As well as letters and symbols you see on your keyboard, you can type a bewildering array of special characters. You may already be familiar with typing accents such as for café (in that case you either type Option+E then E again or, on OS X 10.7 or later, hold down the E until you get extra options) but you'll find there are many more.
Go to the Edit menu of most apps and you'll see Special Characters at the bottom. This panel gives you access to a huge range of symbols you can drag into your documents. Not all apps or operating systems support them, but these are mostly part of the cross-platform Unicode standard. There are probably more than you see at first, too; click the cog to reveal more.
Emoji (those fun, colourful characters available in OS X 10.7 or later) are a notable exception to this cross-platform world. They're not Apple-only, but your recipient might not be able to see them.
6. Record screencasts
You can record videos of your screen; you might want to record a problem or make instructional videos about using apps on your Mac. Open QuickTime Player and from the File menu choose New Screen Recording. Click the little drop-down arrow to pick the audio source and to choose whether or not to show mouse clicks in the recording. Now you can pick to record either the full screen or just a selection, and once you're done, you can do the usual things - trim, upload to YouTube, AirDrop it to another Mac, or import it into iMovie for more precise editing.
7. Zoom into the screen
Want to see something up close? Hold the key and scroll up with your mouse or trackpad. If that does nothing, check the option is enabled in Accessibility, where you will also find options for smoothing and whether you want the whole screen to zoom in or just show you the zoomed area in a little window within your Mac's screen.
8. Slow down animations
Lots of visual effects on your Mac can be slowed down either to help you better understand what's going on, or just so you can go 'oooooh, pretty!'. Hold down Shift when, for example, minimising windows, triggering Mission Control or Launchpad, and you'll see the effect.