I knew this was going to be challenged, and you're not wrong. But Twitter still feels closest to the original incarnation of 'here be a (roughly) reverse-chronological list of text-message length posts'. They had the timeline, the "friend feed" first, and most enhancements affected only the payload of their messages. Moments was a big innovation, and it's presented as a separate offering on their website.

Whereas Facebook's primary function went from a carefully-curated yearbook-style personal and interest page to an... algorithmic timeline of friend's status updates and tumble-blog reposts.

Snapchat went from an app that sends disappearing photos to a general-purpose multimedia messaging app that happens to still put a timer on photos.

Instagram went from a photo and selfie-sharing app to a general-purpose social network with an algorithmic timeline, sponsored posts, and private messaging.