- `Arg`, `Flag`, `Opt` annotations.
- Custom short names for `Flag` and `Opt`.
- Custom prefix characters for `Flag` and `Opt`.
- Default values for `Arg` and `Opt`.
- Automatically generated help page.
- Commands, subcommands, subsubcommands, etc.
- Primitive types, e.g., `Arg[int]`.
- User-defined types, e.g., `Arg[Money]`.