The developer told me they've been using Inkscape, Krita, Godot Engine, GIMP and also Blender to build the game. It's inspired by games like Game Dev Tycoon, but it sounds like it will feature much more in-depth features. You will have the ability to buy and sell studios, decorate your studio, hire developers/designers/testers and so on.
If you want to see some behind the scenes work, they've been developing some of it live on Twitch. Very interested to see what it's like when it's ready! It will release sometime in June next year.