With the founding of MicroPro International in 1978, he became a pioneer of personal computer software, publishing the popular word processing package, WordStar.
WordStar was the first truly successful program for the personal computer in a commercial sense and gave reasonably priced access to word processing for the general population for the first time.
Following his success with this and other related projects, he moved to New Hampshire to be put in charge of the computer software development for a line of IBM compatible programmable CRT terminals.
Two years later, Rubinstein moved to the Bay Area and landed an assignment to implement a law office management system on a Varian Data Machines minicomputer.
As a consequence, Rubinstein temporarily moved to Zürich, Switzerland to utilize the technology he developed as part of a branch banking system for Credit Suisse.
A year and a half later, several IMSAI employees joined Rubinstein at Micropro, including Bruce H. Van Natta, A. Joseph "Joe" Killian, Dianne Hajicek, and Glenn Ewing.
In a Video History Interview with David Allison of the Smithsonian Institution, Bill Gates referred to Rubinstein as starting one of the first software companies [2].