Jet Set Willy
Jet Set Willy is a computer game originally written by Matthew Smith for the ZX Spectrum home computer. It was published in 1984 by Software Projects and ported to most home computers of the time.
The game had some differences on various platforms, but there was always impossible triangle on the title screen. Several screenshots of title screens are presented below. Also, impossible triangle is depicted on cover of ZX spectrum cassette (above).