Software

Some links to software which I recommend for working in GNC!

Free Software

GMAT
A fantastic open source package which does everything from propagation to trajectory optimization and more!
Visual Studio Code
Another fantastic open source package, this time a software development IDE. Easy to use, multi-platform, just works!
Python
One of (if not the most?) powerful free languages available, and has a huge ecosystem of free modules and extensions. Not the most robust set of tools for GNC algorithm development (in my experience), but great for data analysis and visualization, as well as automation.

Commercial Software

MATLAB
MATLAB, with the Control Systems Toolbox and Signal Processing Toolbox should be mandatory for every GNC Engineer. It's possible I've spent more hours in MATLAB than asleep in the last decade.
GitKraken
If you're like me and are fed up resolving merge conflicts at the command line, then this is my go-to Git GUI.
STK
The industry-standard package for everything you could want to model, analyze and design with a spacecraft.
ODTK
If you are doing any flight dynamics, then you need the Orbit Determination Toolkit.
ASTOS
Trajectory optimization for launch vehicles.
DCAP
Great for Rigid Body Dynamics (RBD) analysis.
Kerbal Space Program
You may laugh, but this is how I learnt to be a GNC engineer before I started at Rocket Lab!