Meaning classes, algebraic data types, pattern matching, boxed objects, iterators and garbage collection. All they need is smart pointers or a borrow checker and it'd practically be C++ or Rust, except it's rather brittle because it's just a bunch of macros.

Their FAQs say that's unlikely:

> Is anyone using Cello?

> People have experimented with it, but there is no high profile project I know of that uses it. Cello is too big and scary a dependency for new C projects if they want to be portable and easy to maintain.