Both writer Katharine Davis Fishman, in her 1981 book The Computer Establishment, and computer science historian Martin Campbell-Kelly, in his 2003 volume From Airline Reservations to Sonic the Hedgehog: A History of the Software Industry, have considered ACT an exemplar of the independent, middle-sized software development firms of its era, and the Charles Babbage Institute at the University of Minnesota has also viewed the company's history as important.

[4] Lecht, in his late twenties at the time, was a mathematician and entrepreneur whose involvement with the computer industry dated back to the early 1950s,[3][4] including stints at IBM and the MIT Lincoln Laboratory.

[5] The new firm's first job was fixing a language compiler on the UNIVAC LARC computer, which was being used by the United States Navy.

[6] UNIVAC awarded a $100,000 contract for the work; Lecht hired some programmers and the company's first office was in former servant quarters atop the Plaza Hotel.

[7] As the 1960s went on, ACT built a customer list of established companies and developed a reputation for delivering quality work on schedule.

[6] In September 1964 the company leased regular office space,[8] the first of several locations it would have during its lifetime, all of which were within greater Midtown Manhattan on or near Madison Avenue.

[9] With few trained computer programmers available at the time, Lecht hired those with musical, linguistic, or mathematical backgrounds, finding them to be successful at this new activity.

[10] The firm also did other system software as well as scientific programming projects, including some for the defense industry, and then started doing commercial applications development for large companies such as Union Carbide, United Airlines, Hoffman-LaRoche, and Shell Oil.

"[11] Lecht was a colorful and flamboyant character with an idiosyncratic sense of style, who went around on a motorcycle and was described as a "showman" by colleagues, customers, and competitors alike.

[17] The company also published A Guide for Software Documentation in 1969, compiled and edited by Dorothy Walsh, which was again one of the first of its kind and was cited by a number of other publications in the years to follow.

[13] Entitled Paean, and with album sleeve text bemoaning the loss of the company-mindedness of the 1930s–1950s, it was released via Skye Records in 1969.

[12][16] The eccentricities of the president were balanced by the firm's second-in-command, executive vice-president Oscar H. Schachter, a lawyer who had graduated from Yeshiva College and Harvard Law School and who had a more straight-laced personality.

[27] The initial public offering was handled by boutique technology underwriter Faulkner, Dawkins & Sullivan, and the stock value increased almost four-fold during the first day of trading, ending with a three-fold gain that The New York Times termed "spectacular".

[29] It began a course of diversification beyond consulting and software development[12] by acquiring, in 1969, Rhode Island Lithograph, a printing company in the state of Rhode Island (that was owned by Lecht's brother Danny), and Informatab, a data processing market research company, and by opening Inter-ACT, a training and education arm[30] that wrote computer help manuals that were sold to schools and businesses.

The company also began entering the packaged software business, developing compilers and related tools as a product.

[36] Over time IBM withdrew from that market and the regime of Shah Reza Pahlavi decided to standardize on the Honeywell 6000 series for the Iranian military.

[43] But Wang Laboratories captured much of this word processing market; the Ultratext product may have been overly complicated and Schachter later lamented that ACT letting the opportunity to make an impression in this domain slip away was "one of our worst failures".

[45] It still had its idiosyncratic characteristics; Lecht spoke publicly about a psychologist who visited ACT to discuss employee complaints, saying it saved him two days a week worth of work and predicting it would become a future corporate trend.

[26] Several business, including the service bureaus, were losing money, and there were significant cost overruns developing a set of Pascal compilers.

[26] By Schachter's later telling,[47] the San Francisco investment firm Birr, Wilson made a capital infusion into the company and placed a member on the board of directors.

[48] When it happened, Lecht portrayed the split as his own choice to the press, saying he wanted to pursue writing, speaking, and other activities related to technology.

[26] (A few years later, Lecht said he had left because he became saddened watching the company spirit he had established turn into what he called a "bureaucracy of yuppie nincompoops".

[50] During the rest of 1982, the company sold off its two main service bureaus, those in Phoenix and Edmonton, and closed down two smaller money-losing businesses.

[52] General Dynamics became the biggest customer for the JOVIAL product,[35] especially for its use in the avionics for the F-16 Fighting Falcon, but it was sold to a number of other defense contractors as well.

The cash infusion from Prudential-Bache was also used to develop a compiler system for the Ada programming language, targeted to the MIL-STD-1750A architecture.

[58] Another motivation for ACT entering into the agreement was to gain access to LSI Logic's sales and marketing operation, which was much larger than its own.

[7] Near the end of that decade, all of CSM's applications were converted to being implemented using the MUMPS programming language, which went on to become a common choice within the healthcare industry.

[7][51] For the most part, CSM operated independently of the rest of ACT's activities, but there were occasional collaborations, such as when the parent produced MUMPS implementations for the Digital Equipment Corporation PRO series microcomputers and Tandem Computers NonStop fault-tolerant product line,[68][7] or when ACT's Network Processor product was used underneath CSM's Human Services Network Information System.

[69] In 1989, CSM stopped sharing physical facilities with the rest of ACT, and relocated to Islip, New York on Long Island.

[72] As for Schachter, he went into private practice as a lawyer wherein he provided counsel to several companies in the technology area,[73] and also served as vice president and secretary of the board of directors of American Friends of Yahad-In Unum.