This is a grammar package for the Atom editor. It is meant for email composition based on "netiquette" that has made handling email easier for decades. This package comes with reasonable defaults for line length, tab style, quote-level highlighting, etc. but these settings can be customised, should you so desire. It also includes a basic cleanup-text-feature.
Please see this Wiki for more information.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.