Brackets is a very easy to use, pretty light-weight but very powerful HTML, CSS and PHP editor; it's actually made by Adobe, but it's 100% free and a better - less bloated and confusing - alternative to Dreamweaver and Notepad++ and similar editors. The program is no longer being developed or updated, but it's absolutely reliable and never crashes (I saw it crash only one time on Windows, never on Mac, and I've been using it for a few years now). It has the same features as Nova Editor and WeBuilder, and it's my secondary editor...on both Mac and Windows. Definitely a must-have.
Visual Studio Code is an alternative to Brackets -- in case you prefer to use a program that's still under development (Brackets' stopped in early 2022) -- for editing HTML, CSS and PHP files; it's also a powerful code editor for pretty much any kind of language, from javascript to python. It's cross-platform, owned by Microsoft (so you can count on the development going on for a bit longer), has tons of plugins to add extra functionalities (has a portable version if you want to try it without installing it) and the interface is very minimalistic which makes it fairly easy to use. Plus it's 100% free, so definitely worth at least checking out.
Affinity Photo is, like Pixelmator above, a very strong alternative to Photoshop; the UI is pretty easy and takes little time to get used to - you'll be set and ready to go after just a couple of tutorials; the apps has everything you need to make or edit your graphics and photo, and many feature are easier to modify than Photoshop's. It has a sister app called Affinity Designer - a powerful Illustrator alternative you can use to create stunning vectors and designs - but I've never used that, so I can't really tell you how it is; what I know is that the app is not very cheap priced at around $60 (both Mac and Windows version have the same price) but, considering its features, it's definitely a bargain.
XNViewMP is a pretty good editor perfect to make quick modifications to your photos without having to open Photoshop or similar; the features are not super-advanced and don't allow for heavy layered alterations - that's also because the program has no layers option - but if you need a nice and light-weight editor to do basic changed XNViewMP is a very good tol. My favorite feature is the one that allows you to create a header base with a few clicks (as shown in this tutorial), but the other features are quite nifty. The program is 100% free, and it's a handy tool to have on your computer.
FileZilla doesn't certainly need an introduction as it's probably one if not the most used FTP client, but I bet many Windows users didn't know or overlooked the fact that it's a cross-platform program...meaning that, if you were used to working with it on Windows, you don't need to scramble looking for a Mac alternative but can just go ahead and keep using it. I personally don't like the Windows version (as it made 2 of my computers nearly crash), but the Mac version is sleek and works as a breeze. It's definitely another must-have app for your pc.