Messenger

Messenger's most-copied contribution was the chat head, a floating bubble that let a conversation hover over any other app, treating a thread as something that follows you rather than a destination you visit. Its identity is the Facebook graph: you don't add contacts so much as inherit them, which makes reach effortless and unsolicited-message friction real. The interface piles on expression, with reactions, oversized animated emoji, GIF pickers, and per-thread color and nickname customization that make each chat feel skinned. Active-now dots and last-seen timestamps keep presence front and center. Over the years the app accreted Stories, payments, games, and shortcut tabs, and that feature sprawl is the recurring critique: a simple message can be three taps from a screen busy with everything else Meta wants you doing.