How to improve your Mac OS X workstation
There are quite a few tools available to help you to get most out of your macOS workstation. Darwin, the macOS base system, is a BSD on Mach Microkernel and this gives you the possibility to use nearly all of the typical OpenSource applications written for Linux or BSD. Furthermore, a lot of Freeware for macOS is provided by various people. Lastly, you may also opt for commercial applications like MS Office or the Adobe products.
LibreOffice is a free office suite for word processing, spreadsheets, presentations, and more. It can replace Word, Excel, PowerPoint, and Access.
If you need Microsoft Office (Word, Excel, Powerpoint, Outlook,...), you may order it from IDES.
PDF Reader and Writer
Apple's Preview is the standard MacOS application to view and annotate pdf files. If you want to create a PDF file you can do that without additional software using the standard print dialog. If you want you can additionally install Adobe's Acrobat Reader (proprietary, free software) or the complete Acrobat application (proprietary, for ETH use purchase it via IDES)
Skim is a very powerful alternative to view and especially to annotate pdfs.
Mozilla Thunderbird can be used as an alternative email client to Apple Mail.
VLC is a versatile video and audio player that knows about a lot of different audio/video formats and can play from files or internet streams. It is a nice addition and complement to Apple's QuickTime and iTunes.
Adium is a instant messaging (one-to-one chat) client that understands more protocols than Apple's iChat. On the other hand it cannot do video chat like iChat does.
Google Earth allows you to explore the globe of our earth and obtain a wealth of geography related information.
Cyberduck is a front end to transfer files to and from servers, via various protocols.
Developer Tools and Unix Ports
Developer Tools (Xcode)
Apple offers a full set of development tools called Xcode. Even if you don't develop applications, the Developer Tools are needed for MacPorts as they provide compilers and several tools to maintain your system.
http://hpc.sourceforge.net hosts a number of compilers and computation tools for the Mac.
Emacs is one of the most powerful editors.
iTerm2 is a powerful terminal emulator providing many more features than the standard Mac OS Terminal.