vi

Linux Mag asked Bill Joy (creator of VI): “So you didn’t really write vi in one weekend like everybody says?”

No. It took a long time. It was really hard to do because you’ve got to remember that I was trying to make it usable over a 300 baud modem. That’s also the reason you have all these funny commands. It just barely worked to use a screen editor over a modem. It was just barely fast enough. A 1200 baud modem was an upgrade. 1200 baud now is pretty slow.

http://www.theregister.co.uk/2003/09/11/bill_joys_greatest_gift/