I am New to Mac; What are the Must-Have Apps?

This is such a loaded question and the responses will vary depending on the responder. Personally, I am very security-minded thus I have Little Snitch, Hands Off!, Murus Pro, 1Password, Knox, Espionage, BCWipe, BestCrypt, just to name a few. Redundant back-ups are also imperative to me thus I have both Carbon Copy Cloner and ChronoSync with ChronoAgent in case I need it one day. That is just me and that is only an introduction to what is on my digital fortress. To more effectively respond to your question, I will do so in sections pertinent to your potential requirements.

Bootable Clone, Back-Up and Synchronisation:
It matters not what kind of Macintosh you have; it must have at least one redundant back-up and preferably one off-site back-up. To accomplish both I wholeheartedly recommend ChronoSync [and ChronoAgent] for on-site and off-site back-ups. Imagine you are a year into your usage with exact customisations in place but depend on the machine and its data every day. One day it unexpectedly fails to boot. No desktop, no finder, nothing passed the kernel check. Goodbye files. ChronoSync will be your lifeline because, after the time it spent to configure the program, run your first back-up and subsequent incremental back-ups [test your back-up every two months!], you will be operating your machine as you were before the catastrophe in minutes. I mentioned Carbon Copy Cloner because it most likely will be more easy and straightforward for you though it requires some configuration though less than ChronoSync. ChronoSync is also perfect for too many synchronisation configurations to explain here but whatever it is you can synchronise it with ChronoSync.

Security:
Amongst many in the know, I often question the thought processes of Apple's Mac OS security team. Surprising as it may be [and it is to me every time I read about it], users are completely unaware that a firewall disabled by default is available in System Preferences | Security and Privacy | Firewall tab. Firstly, enable that – no questions asked. If it is unnecessary it would not exist. Enable the stealth setting on the options panel by activation of the Options button on the same panel to enable the firewall. That is all good but again I question the employees of Apples' thought processes. As effective as the packet filter [PF] firewall is it has no front-end. Murus Pro [free will suffice here I guess] provides a full-fledged graphical user interface to control the built-in firewall to unleash the full capabilities of it. I also mentioned Little Snitch and Hands Off!. They are even better and more effective firewalls but the pop-up dialogues to allow or deny connections seem to annoy many. The purpose is to know and note what programs contact outside servers also known as phoning home. It also allows or denies incoming connections which makes it a full-fledged firewall. Little Snitch initially disables GUI scripting which must be enabled by a sighted person via mouse or trackpad because without GUI scripting the keyboard is unable to be used. Hands Off! does not require this and also permits or prohibits programs from reading and writing data to disk. The pop-up dialogues still exist and are necessary in any program of this kind to provide the user the tools to allow or deny a connection. I mentioned 1Password. There are a myriad of programs in and out the app store that do what 1Password does but not one does it as well and robustly as it. I store everything in 1Password from log-in data to software license and registration data to bank information and even miscellaneous product orders that have an attachable invoice. Best of all, the vault is encrypted with more safeguards than any other program of its kind. It gets no better in that category. Also from the same company is Knox. True, Disk Utility can also make encrypted disk images but Knox does it with less keystrokes and makes use of a different type of disk image called a sparse bundle which can be split. I also mentioned Espionage which, despite the horrible and contradictory name, does the same as Knox. The take-away difference is Espionage employs something called plausible deniability. Not one other program of its kind to my knowledge has this obvious advantage. If you are curious what that is I encourage further research. You have a portable Macintosh so it can be stolen at any second when not under your supervision. A small program called Plug-Spy can assist to identify the perpetrator by taking a photo via the built-in camera, sending Pushover notifications/boxcar notifications/local notifications and more. It uses sensors including the MagSafe method used to recharge the battery amongst others. My choice of anti-thievery program is actually a preference pane called RedHand [think caught red-handed]. It is similar but the interface is more straightforward and almost everything has a help tag that explains its function. That is free and I encourage its use. There are a few others I did not mention but those should suffice for this section.

Audio recording:
Recording, not editing. Seek no further than Audio Hijack. It has existed since year 2002 and is now better and more accessible than ever. VoiceOver compliance was an integral part of the latest major iteration and they pulled no punches. As highly visual as the interface may be, it works flawlessly with VoiceOver. Record anything audible that comes to mind [program, website, system et cetera] in an array of formats with attributes fully customisable. Audio Hijack is impossible to disappoint. After recording is finished the files can be merged with their other program called Fission. Anything more than that I recommend Logic Pro.

Media Players and Transcoders:
There are an array of media players for Mac OS X but my recommendation is MPlayerX. It is free and plays every format of video file and codec imaginable. I personally transcode from DVDs to Matroska [MKV] files using the H.265 (x265) codec and pass through the audio bit for bit with all channels. I personally despise iTunes and always have. MPlayerX puts iTunes to shame. The controls are unlabelled but basic operation is possible. Elmedia Pro is based on MPlayerX but also allows to download video and/or audio from YouTube and any other website that streams the content. Again the controls are unlabelled but basic operation and downloading is possible. If you transcode seek no further than HandBrake. It is free, accessible and constantly improving. Another very useful utility that has been in existence since 2003 is called xACT which stands for X Audio Compression Toolkit. Over a decade back, there was once a popular audio format called Shorten [SHN] which was popular amongst those who traded recordings of live concerts. The populous of today's generation have no clue what Shorten is but it still lurks in the shadows of Free Lossless Audio Codec [FLAC], Monkey's Audio [APE], OptimFrog [OFR], Apple Lossless Audio Codec [ALAC] amongst other fellow lossless compression audio file formats. xACT converts all these including the lossy ones like MPEG layer-3 [MP3], Advanced Audio Codec [AAC – think M4A], OGG Vorbis [OGG] et cetera. It uses the seasoned veteran LAME encoder to encode MP3, and unlike other programs, has the ability to customise the Q# setting that is almost command-line exclusive. This makes the world of difference. xACT is free and reliable.

Efficiency and Automation:
We Macintosh and Mac OS power users separate ourselves from the great unwashed masses of users of the same machines and operating system in several ways. One of which is by using programs which save time, keystrokes [which also saves time], eliminates repetition [which in the end saves time] and basically does the work once done manually for hopefully not too long. That is what TextExpander does for me. For years I used to type the same boiler plate phrases, sentences and paragraphs. The monotony ceased when I began to use TextExpander. I have every boiler plate symbol and piece of text saved with abbreviations to accompany them. How do you think I type these keycap symbols? To type the abbreviation [I just typed the letters a-a-b-r and so expanded the word abbreviation – see how nice and refreshing that is?] will unquestionably save so much time – even if just a large word that you will download to your iDevice as well. Best of all, my settings are synchronised thus I can save even more time on my iDevice by using the same ever-growing library on-the-go as folks say. If that fails to save you sufficient time LaunchBar most likely will. From the fine folks who develop Little Snitch also develop LaunchBar. Think what Spotlight would be if it was fifty thousand times more capable. That means fifty thousand times more useful. Possibilities are almost infinite with LaunchBar and I honestly do not know where to begin. I seldom type ⌘-⇧-A or U to enter the Applications or Utilities folders because an arbitrary abbreviation will find the program and a press of the ⌤ key will activate it. Is the ⌘-⇥ key combination not optimal as an application switcher? LaunchBar takes care of that by allowing applications to be switched by holding the ⌘ key and pressing the Space bar. It also has other window-switching capabilities and such. If you just can not be satisfied with those try Keyboard Maestro. It is NOT for the faint of heart. Macros and imagination equals almost infinite amount of possibilities. This is like LaunchBar on steroids with the steroids on crack. If you want power, Keyboard Maestro provides you with unmatched power that will save you so much time… Alas, I will ‘tone it down’ considerably and recommend something I and many others use to do the mundane tasks such as housekeeping. Speaking of housekeeping, I have a housekeeper and her name is Hazel. She is a preference pane and a highly customisable one too. She does many things but Windows is not one. Somehow, some way, for some reason[s], users seem to have cluttered Downloads folders. If that is the case, Hazel will clean up the Downloads folder… or any other folder. Trash does not bother her either and when I heard the news I put her on an hourly schedule to take out the trash or delete immediately if a file is above a certain threshold. Even AirDropped items can be moved from Downloads to elsewhere [there is no other manner by which to select the destination of an item sent via AirDrop]. Give Hazel a chance and you just might keep her around. I abducted her and will hold her hostage till she dies and transcends to the great digital mausoleum, wherever that may be.

Though it was but a handful of programs for power users and novices alike, I hope that assists to accomplish whatever it is you wish on your machine. Finding the perfect program for everything is a never-ending saga as is customising the operating system down to the manner by which the system boots [normal verses verbose]. It was my intent to preclude programs that make changes to features and functions you probably are unaware that exist but to be a Macintosh and Mac OS power user comes with time.

From 1984 till 2004, Mac OS had no infections of any kind. From 2004 on the operating system has experienced its fair share of viruses and malware. Many former Windows users swear to the fact Mac OS users need this and that but it is simply not true. Whilst it is true exploits can be taken advantage of, the infection rate amongst users of Mac OS is much lower than those of Windows. Mac OS users are usually the carriers who deliver and/or distribute the malicious code. However, it never hurts to install a renown anti-virus security suite and the one I recommend is any from ESET. They make stellar products for both operating systems and all work quite well. Research products from ESET in the Home section.