In 1993 Urban Müller uploaded a 240-byte compiler for the Amiga to Aminet, with a readme describing a language of eight commands and the challenge "Who can program anything useful with it?" The archive included a few example programs. This is its hello.b.
The eight commands move a pointer left and right along a tape of cells, increment and decrement the cell, read and write a byte, and loop while the cell is nonzero. Nothing else exists. The program builds each letter by counting up in a loop, prints it, and clears the cell. The lone # in the middle is a debugging command in Müller's interpreter, which dumped the tape. The hello world that circulates online, beginning ++++++++[>++++, is a later community rewrite and is not in the archive; this is the author's own. Brainfuck proved that a language can be Turing complete and still fit in a tweet, and it started the field of esoteric languages, where the point is to find out what a language can be when it refuses to be useful.