Not even remotely close. If you have millions of dollars and lots of talented programmers, I can build an engine from scratch. We do not live in an ideal world - public policy is about the art of the possible, and $19.99 (cost of Skylines in Sri Lanka) is a massive improvement from the $8000 a year fee for CUBE or OpenPaths. I do want to build a sim someday, but I estimate the learning of it will take me a few years to complete. Right now I'm at the stage of writing basic galaxy generator toys like https://github.com/yudhanjaya/GalaxyGen

This is super impressive! I'd agree the open-source tooling isn't there yet, but it's coming in a few places. I started a 3D street visualizer but it's only at the scope of a few blocks at a time, not as large as a city area although we'd like to get there someday: https://github.com/3dstreet/3dstreet/

There's also https://github.com/a-b-street/abstreet for larger area simulation but with less visual fidelity

Very cool, great to see progress in this!