Having never heard of this, I found the FAQ page an informative starting point. https://clean.cs.ru.nl/FAQ In simplistic terms, Clean seems to be a “better Haskell”. Edit: I just downloaded the bundle tar, looked at some sources and found out that vim has syntax coloring for Clean out of the box. Vim never ceases to amaze me. More Edit: Clean transpiles to C, which means that when you look at generated code, or just…
It's a pity this info is so hard to find. I had to click for a minute to find some example code, and thought: this is very much like Haskell. I wonder how it's better than Haskell, why not Idris/Coq/Adga, and why not contribute to any of the just mentioned projects. This info, combined with some code and a description of the target audience of the project would be very helpful indeed.
I don't think anybody claims it's better than Haskell. It predates it, for one. The Clean programming language is its own thing, with its own philosophy, uniqueness types, etc.
Don't be mislead by the usual online flamebait trying to turn everything into "X is better than Y". This is usually claimed by people with little experience in either X or Y.