GroundPlane

Literally C/C++. Most used out there. Now if you want to do everything with it, you're in for a long ride. You can do everything on every platform with C. But learning the language is the easy part. The hard part is learning good coding pratices, which library to use and how. Only guides and practice will help you there

1. Turning into an executable is compiling as far as C goes. For Python, there probably is something somewhere to wrap a script into a .exe.

2. For the UI: what matters is the data you generate, not the fluff around it. As the other commenter said, start with a CLI program. You can easily nest several levels of menus if that's your thing. This allows you to have user input. Then for outputs you can do it to a .txt or .md file. Use simple text-based formats. Then once you've got that down you could build a GUI? But tbh I have never built a GUI and I've been programming for 10 years at this point so I can't help you out. There are simple cross-platform libraries you can use out there