My favourite part of setting up a new computer is installing applications. It's a great opportunity to revaluate what applications you currently use, and try out alternatives.
The Dock is a great place to start, as that is where my most used applications live.
iTunes - Surprise surprise, I use this for music & movies. I don't store much locally, as most of my music streamed via iTunes Match. Also there are countless movies that I have acquired over the years from iTunes.
iBooks - I've only just started using iBooks on the Mac, mainly for reading documentation, such as The Swift Programming Language. I still don't enjoy reading novels from a laptop, so I stick to my iPad for that.
Safari - My favourite way to browse the web. I love that Keychain creates, saves and syncs unique passwords for me across the web straight to my mobile devices. More recently, I have ditched my regular RSS reader and Instapaper to make use of Safari's Shared Links and Reading List. So far, it is working well. I especially like seeing links from the people I follow on Twitter show up in-between my RSS items.
Note: RSS Subscription are only available in OS X Yosemite & iOS 8 versions of Safari
Tweetbot - My favourite Twitter client. It syncs my reading spot with its mobile counterparts, along with mute lists.
Sketch - I've always used Adobe's creative suite's for graphic design, but I've never loved using it. I am trying to steer clear of Adobe's software as I've found its very bloated for my simple needs, occasionally buggy, expensive with subscriptions... Basicallly, I don't find myself to be the market Adobe are trying to target. Enter Sketch. A beautiful, lightweight design tool made from the ground up for Mac. It also has an iOS app called Sketch Mirror, which allows you to beam the workspace you are currently working on to an iOS device, great for when working with UI mockups.
Xcode - If you don't know that Xcode is, chances are you don't need to know, but for the curious, its a tool that Apple releases that allow developers to create rich applications for OS X & iOS. I am currently working with the latest beta, getting deep into the new programming language that Apple released at WWDC earlier this year. My favourite new feature has to be Playgrounds. It is just so fun to use when prototyping segments of code, mainly due to the real time feedback it gives you as you write.
Home Folder - Ok, so not an application, but it allows me to instantly look at the root of my home folder.
Trash Can - Such a pretty icon in Yosemite, don't you think?
Currently Missing: I have yet to settle on a writing application for OS X and iOS. Writer.Pro was my previous favourite, but I am going to do a little research and look for an alternative. A great photo management application is also missing. Over the years I have amassed just over 150gb of photographs, which need a home. I have decided against my previous tool, Lightroom, due to my Adobe boycott, although the alternatives are not much better. Apple's very own iPhoto and Aperture has been discontinued and are due to be replaced by iCloud Photo Library, which I think I will transfer to in future, although there is no OS X app for it yet.