Anyone using a DAW nowadays should be familiar with MIDI instruments and the Piano Roll (#blessed). Before the Piano Roll became a staple in music production, explorers in electronic music relied on step-sequencers of all types.
The earliest analog step-sequencers were used in player pianos which were fed rolls of paper with holes punched into it to tell a piano which notes to play, hence the 'Piano Roll'. Software step-sequencers were developed for and have been used in computer music since the 1950's, allowing for composition, playback, and sound synthesis. In the 1980's we saw the invention of Soundtrackers which were some of the first software step-sequencers to allow for complex music production.