Folk UI

User-interface conventions, invented by individuals from scratch, that went on to become actual norms.

hashtags

Invented by Chris Messina (q.v.)

Name coined by Stowe Boyd (American Dialect Society Word of the Year [q.v] for 2012)

microformats

Arguably the O.G. folk UI, and almost certainly invented by Tantek, inserting values into rel and rev attributes according to loosely-agreed-upon rules is still being done (e.g. rel="payment" in Overcast)

pull-to-refresh

Invented by Loren Brichter for Tweetie; it is now easier to list where it isn’t used on iOS

machine tags

Used almost exclusively on Flickr and now almost exclusively by me. Didn’t take off as microformats did

house icon to mean homepage

As distinct from skeumorphic floppy disc to mean Save. No officially encoded emoji is a clear candidate here (perhaps 🏠); people tended to use images

Next likely candidate

Procreate’s two-finger single-tap for undo (three-finger single-tap for redo). (As distinct from two-finger double-tap in VoiceOver [“Magic Tap”], which does the most obvious thing – if the phone’s ringing, it answers the phone, &c.)

Not really falling into the category of folk UI

• hamburger menus

• Alt‑Tab (so useful that Macs borrowed it as Command‑Tab)

• right-clicking

(Hat tip: Gruber.)