COSMIC
COSMIC is a desktop environment developed in the Rust programming language, using the iced cross platform GUI library for Rust, and Smithay as building blocks for its compositor, cosmic-comp. Cosmic-comp is comparable to smithay's own anvil compositor demonstration, just like the Wayland project uses Weston as demo compositor.
COSMIC was primarily developed for use in the Pop!_OS distribution.
In Progress
COSMIC support in nixpkgs is still in development. You can follow progress via the tracking issue.
There is a flake to setup Cosmic on NixOS.
COSMIC Packages
While the whole desktop is not configured many packages are available in nixpkgs already. You can search for packages with a query similar to this one https://search.nixos.org/packages?query=cosmic&from=0&size=1000&sort=relevance&channel=unstable. Note that not all of the results will be part of the COSMIC desktop.