In my classification, Tree-sitter is a building block (a parser), not a tool (compiler, editor, highlighter etc.) And as seen in this HN submission about implementing HTML support for Emacs, it's used in M×N integrations.
It's an M+N tool in my opinion because it parses M languages with a uniform interface, for use in N higher-level tools. I can use the same Python grammar/parser with any tool that's based on Tree Sitter.
I didn't know tree-sitter-highlight exists though. It seems to provide M+N highlighting and includes a CLI tool. https://tree-sitter.github.io/tree-sitter/syntax-highlightin...
Similarly, tree-sitter tags seems to provide M+N code indexing: https://tree-sitter.github.io/tree-sitter/code-navigation-sy...