The primary feature is speed. We designed Zappy to work "in flow" and minimize the number of keyboard/mouse interactions. The critical path is: cmd+shift+1 (or whatever shortcut you want) -> drag a box -> press "enter" to immediately get a shareable image (or URL for paid) on your clipboard.

In addition to speed, it's an all-in-one tool that does annotations, GIFs, and screen recording (with optional audio and selfie camera) and we optimized those flow for speed, too.