This is not it. It's a desktop IDE built using dotnet that just assembles 6502 instructions with some extra awkward syntax.
Many more elaborate projects exist. My favorite is the one that compiles something similar to Turbo Pascal to C64 6502. It's implemented in C++/Qt, but noone ever tried to market it that way, because why would they?
Turbo Rascal Syntax Error
It depends on the purpose. The reference IDE is intended to produce real-world programs (it includes tools for sprites, music etc.), while high level language compilers are mostly academic, as they're not performant enough.
There isn't a multiplication instruction, so you have to painstakingly reinvent all useful algorithms from the last 40 years from nearly scratch and by the time you want to implement a hash you notice you're running out of RAM.
Because of the lack of a multiplication op code? Hmm.
Multiplication instructions and hash tables (!) are easily worked around, as evidenced by decades of art and innovation programmed on that "terrible" CPU. There are still 6502 programmers today delivering games, art, demoscene, etc.
That CPU was a foundation of the home computer and console revolution: BBC, Commodore, Atari (consoles and computers), Apple, and Nintendo (NES).
All the three of games/art/demoscene on something like the C64 have a rough idea as the spec, but then you'll get creative about how much of that "spec" you can bend and violate to meet the technical limitations of the C64, while still being fun.