[arp242]

It's in the standard library for Python, Rust, Julia, and maybe some other languages. It's also widely used in those ecosystems (pyproject.toml, cargo.toml). I think it's fair to say it took off, even though YAML is also popular.

[jononor]

The tomllib library in Python 3.11+ can only read TOML files, not write them.

[dagenix]

I don't believe its in the standard library for Rust, even if it is very popular in the Rust ecosystem.

[arp242]

Right; I'm not super-familiar with Rust and how exactly they organise things, but it's in more or less every Rust project due to Cargo.toml.