Better Unicode support in the regex engine. More flexible ignore rules (you aren't just limited to what `.gitignore` says, you can also use `.ignore` and `.rgignore`). Automatic support for searching UTF-16 files. No special flags required to search outside of git repositories or even across multiple git repositories in one search. Preprocessors via the `--pre` flag that let you transform data before searching it (e.g., running `pdftotext` on `*.pdf` files). And maybe some other things.

`git grep` on the other hand has `--and/--or/--not` and `--show-function` that ripgrep doesn't have (yet).