Way back in 1995 when the personal computer was barely a thing, Robert Henke and Gerhard Behles (now the CEO of Ableton), created Monolake. Monolake's PX18 sequencer is a step sequencer and timeline with a multitude of mathematical-musical features. The PX18 as a software has left an iconic legacy as the sequencer that inspired Ableton.
The PX18 is theoretically still available for download and use, although it is definitely outdated now and would probably cause more stress than relief.
The PX18 is historically important for two main reasons. One, it offers a look into the imagination and innovation of Monolake, as the template would eventually become the basis of IDM (Intelligent Dance Music). It's about the groove, but with options for compositional choices that would make each song unique. Two, the PX18 is widely accepted as the technological and aesthetic predecessor to Ableton Live. The ideas Monolake used as musicians with the PX18 formed a testbed and gave Gerhard and Robert the insight necessary in forming Ableton just a few years later.
The PX18 even has some features that Ableton does not, such as rotational compositional shifts that focus more on variation rather than triggering. This shift can be heard in Monolake's earlier music compared to their (Robert's) more recent productions. Robert and Gerhard took their technological and musical knowledge and combined them to make a tool suited just for them, that would end up defining a generation of musicians.
This interesting piece of history is still going strong, even if no one is using it. The PX18 sequencer has solidified its place in the history books of electronic music and we wouldn't be where we are now without it.