Mac and Mathematicians

Quicksilver: This is the first thing I would install in any Mac. Allows you to execute various things (applications, files, folders, bookmarks, etc) with a few keystrokes. (After installation, check out this page.) El Capitan’s Spotlight search is getting close to Quicksilver, but it doesn’t (yet) allow to choose your “action” with the selected item.
MacTeX: This has all the necessary files to start typesetting with $\TeX$. It includes TeXShop as the front end. (Link to local documentation: copy and paste this link. Hat tip: Warren Siegel)
PDF to Keynote (Obsolete since Mountain Lion): ‘PDF to Keynote’ converts PDF slides to a Keynote file; this allows me to use my Apple Remote to present the slides I created with $PDF\LaTeX$. (Preview, so far, cannot be controlled with Apple Remote, but Keynote can be and it doesn’t require registration if I use it for presentation only!)

Yummy FTP: I tried Cyberduck, Fetch, Transmit; but Yummy FTP is my choice.
TotalFinder: Especially appealing is that TotalFinder makes “dual mode” available, in which the contents of two folders are displayed side-by-side in a single window. Such functionalities are also provided by PathFinder (Finder on steroids, I call it); but I find it slow, expensive, and heavy to carry around. Besides, the “power actions” I find useful that are provided by PathFinder, I can do much faster with Quicksilver. So Quicksilver+TotalFinder would be my choice for productivity.
Start Up Sound: I’m often in my classroom with my MacBook. Sometimes I have to boot my computer, and once in a while (if I didn’t mute the volume at the time of last shut down) I get the “bing!!!” sound. So I wondered if there’s any way to mute the start-up sound. Startupsound.prefpane not only allows you to mute the start-up sound, but set a non-zero volume of your choice to it.
Magic Number Machine: A simple scientific calculator, handy at some times.

Stripping audio from a video file: Use “Encode Selected Video Files” from the right-click context menu.