Oneliner
The one-line message board on a BBS — every caller got to leave a single line shown to the next, a graffiti wall in real time.
On many boards the login screen greeted you with a handful of lines left by earlier callers: jokes, greets, gripes about the sysop and, often enough, plain rudeness. You added your own line, the oldest scrolled off, and the next visitor saw the result. The space was deliberately tiny — one line forced brevity.
The oneliner was the BBS scene's answer to a guestbook with no memory, a bit of social glue on systems where most callers never met in real time. The tone mirrored the board: rowdy on a warez board, gentle on a hobby one.