As opposed to being a plugin manager, mason is a package manager. It installs editor-agnostic tools like LSPs, linters, or formatters.
As opposed to system-level package managers like homebrew, mason is specifically integrated in nvim. Other than having an UI inside nvim, this entails features such as auto-installing packages when bootstrapping nvim on a new machine.
As opposed to language-specific package managers such as npm or pip, mason includes packages across languages. That means instead of having to install one tool with npm, one with cargo, one with pip etc., you can install all your nvim-related packages just with mason.
While a plugin manager is basically a necessity, mason is more of a nice-to-have tool for nvim. It is convenient for some people, while others prefer using their existing package managers.
What motivates people to keep creating new ones?
I understand the creator's viewpoint (Helix was made the way he likes it), but I think it would have been better to separate out the editing logic from all the other great, overlapping features.
It would be nice to have a modern, modal text editor that allows a user to utilize an uncompromising vim mode, emacs mode, kakoune mode, or any other custom mode they'd like -- all built in natively. An editor built for everyone should not be opinionated about how one edits.
That along with things like a built in LSP, plugin management, and extensible scripting support (allowing the use of plugins would multiple ecosystems) would be really sweet.
What’s mason do that lazy.nvim doesn’t? Especially since it looks like you’re supposed to use lazy to install mason?
mason.nvim is a Neovim plugin that allows you to easily manage external editor tooling such as LSP servers, DAP servers, linters, and formatters through a single interface.
Mason installs and manages things like Language Servers, which are separate binaries running on your machine, and also starts them on demand.