Here, I'll provide links to any useful resources that I make or find.
Anaconda - Free Python distribution with over 300 popular Python packages for any sort of scientific or engineering analysis that you may want to perform. I use this with the Spyder IDE that comes with it, and it has never let me down with functionality. Unlike MATLAB, this is free for everyone!
LTspice - Great free SPICE simulator that will allow you to simulate many straightforward circuits. Don't get too caught up in trying to simulate everything, especially complicated ICs; just build your circuit!
TeXstudio - The current program that I use for LaTeX.
Macvim - My preferred text editor for straight C and miscellaneous code. Simple and works great. Free. To be fair, I haven't tried too many, so there may very well be better ones out there. It's better to get one that you're comfortable with.
Microwaves101 - The go-to website for practical microwave information. Whether using it to learn, or as a reference, it's a great website that's published in association with IEEE.
RF Cafe - Another great RF/microwave resource. Plenty of content and formulas to keep you going.
Antenna-Theory - This website will teach you about antennas, in a practical manner. To quote the front page: "This website will strive to make antennas understandable, without unnecessary complexity."
WolframAlpha - Excellent computational search engine. For high school and university students, and anyone beyond, this is great for checking and solving any maths that you do. Becoming a member gives you access to worked solutions to various questions. This was probably one of the most frequently used websites by my cohort when we were doing pure maths courses.
Okawa Sallen-Key - Easy to use website to quickly design Sallen-Key filters with real components. It gets as close to your design parameters as it can, while prioritising that the filter can be built with real values of components.
Etymonline - Etymology website that I use regularly. My first stop for looking into etymology.
Tangorin - Great Japanese dictionary with example sentences and a good Kanji system. This is my go-to dictionary.
Naver Dictionary - Good Korean resources with solid English/Korean are hard to come across on the Internet, but this one seems the most useful from what I've found.